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This is the amount that we pay to interact and..." template="web-share-button"> </web-share-wrapper> <template id="web-share-button"> <a href="#" class="dropdown-link-row crayons-link crayons-link--block">Share Post via...</a> </template> <a href="/report-abuse" class="crayons-link crayons-link--block">Report Abuse</a> </div> </div> </div> </div> </aside> <main id="main-content" class="crayons-layout__content grid gap-4"> <div class="article-wrapper"> <article class="crayons-card crayons-article mb-4" id="article-show-container" data-article-id="1056635" data-article-slug="gas-saving-techniques-in-solidity-324c" data-author-id="353932" data-author-name="Jamiebones" data-author-username="jamiescript" data-co-author-ids="" data-path="/jamiescript/gas-saving-techniques-in-solidity-324c" data-pin-path="/stories/feed/pinned_article" data-pinned-article-id="" data-published="true" data-scheduled="false" > <header class="crayons-article__header" id="main-title"> <div class="crayons-article__header__meta"> <div class="flex s:items-start flex-col s:flex-row"> <div id="action-space" class="crayons-article__actions mb-4 s:mb-0 s:order-last"></div> <div class="flex flex-1 mb-5 items-start"> <div class="relative"> <a href="/jamiescript"><img class="radius-full align-middle" src="https://media2.dev.to/dynamic/image/width=50,height=50,fit=cover,gravity=auto,format=auto/https%3A%2F%2Fdev-to-uploads.s3.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F353932%2F769950c3-6795-45bb-b2d3-159035ae9430.jpg" width="40" height="40" alt="Jamiebones" /></a> </div> <div class="pl-3 flex-1"> <a href="/jamiescript" class="crayons-link fw-bold">Jamiebones</a> <p class="fs-xs color-base-60"> Posted on <time datetime="2022-07-09T20:12:55Z" class="date">Jul 9, 2022</time> </p> </div> </div> </div> <div class="multiple_reactions_engagement"> <span class="reaction_engagement_like hidden"> <img src="https://assets.dev.to/assets/sparkle-heart-5f9bee3767e18deb1bb725290cb151c25234768a0e9a2bd39370c382d02920cf.svg" width="24" height="24" /> <span id="reaction_engagement_like_count"> </span> </span> <span class="reaction_engagement_unicorn hidden"> <img src="https://assets.dev.to/assets/multi-unicorn-b44d6f8c23cdd00964192bedc38af3e82463978aa611b4365bd33a0f1f4f3e97.svg" width="24" height="24" /> <span id="reaction_engagement_unicorn_count"> </span> </span> <span class="reaction_engagement_exploding_head hidden"> <img src="https://assets.dev.to/assets/exploding-head-daceb38d627e6ae9b730f36a1e390fca556a4289d5a41abb2c35068ad3e2c4b5.svg" width="24" height="24" /> <span id="reaction_engagement_exploding_head_count"> </span> </span> <span class="reaction_engagement_raised_hands hidden"> <img src="https://assets.dev.to/assets/raised-hands-74b2099fd66a39f2d7eed9305ee0f4553df0eb7b4f11b01b6b1b499973048fe5.svg" width="24" height="24" /> <span id="reaction_engagement_raised_hands_count"> </span> </span> <span class="reaction_engagement_fire hidden"> <img src="https://assets.dev.to/assets/fire-f60e7a582391810302117f987b22a8ef04a2fe0df7e3258a5f49332df1cec71e.svg" width="24" height="24" /> <span id="reaction_engagement_fire_count"> </span> </span> </div> <h1 class=" fs-3xl m:fs-4xl l:fs-5xl fw-bold s:fw-heavy lh-tight mb-2 medium"> Gas Saving Techniques in Solidity </h1> <div class="spec__tags flex flex-wrap"> <a class="crayons-tag " style=" --tag-bg: rgba(59, 73, 223, 0.10); --tag-prefix: #3b49df; --tag-bg-hover: rgba(59, 73, 223, 0.10); --tag-prefix-hover: #3b49df; " href="/t/solidity"><span class="crayons-tag__prefix">#</span>solidity</a> <a class="crayons-tag " style=" --tag-bg: rgba(59, 73, 223, 0.10); --tag-prefix: #3b49df; --tag-bg-hover: rgba(59, 73, 223, 0.10); --tag-prefix-hover: #3b49df; " href="/t/gas"><span class="crayons-tag__prefix">#</span>gas</a> <a class="crayons-tag " style=" --tag-bg: rgba(17, 58, 98, 0.10); --tag-prefix: #113a62; --tag-bg-hover: rgba(17, 58, 98, 0.10); --tag-prefix-hover: #113a62; " href="/t/blockchain"><span class="crayons-tag__prefix">#</span>blockchain</a> <a class="crayons-tag " style=" --tag-bg: rgba(59, 73, 223, 0.10); --tag-prefix: #3b49df; --tag-bg-hover: rgba(59, 73, 223, 0.10); --tag-prefix-hover: #3b49df; " href="/t/calldata"><span class="crayons-tag__prefix">#</span>calldata</a> </div> </div> </header> <div class="crayons-article__main "> <div class="crayons-article__body text-styles spec__body" data-article-id="1056635" id="article-body"> <p><code>Gas</code> is a unit of computational measure in Solidity. This is the amount that we pay to interact and transact with a smart contracts. The <code>gas</code> is calculated via a simple formulae which is:<br> <code>Gas = Gas Price * Gas used</code>.<br> The <code>gas</code> price is not constant and it is dependent on the congestion of the network. The more users pushing transaction through the network the higher the <code>gas</code> price. The amount of <code>gas</code> used is determined by the operation performed by the smart contract. </p> <p>This blog post will discuss some techniques we might employ to reduce the <code>gas</code> spent when sending transaction to a smart contract. We will consider the following listed techniques to reduce the <code>gas</code> foot print of a smart contract.</p> <ul> <li> <a href="#constant">Use constant and immutable variables for variable that don't change</a> </li> <li> <a href="#cache">Cache read variables in memory</a> </li> <li> <a href="#incrementing">Incrementing and decrementing by 1</a> </li> <li> <a href="#calldata">calldata and memory </a> </li> <li> <a href="#view">Calling view function </a> </li> <li> <a href="#overflow">Integer overflow/underflow </a> </li> <li> <a href="#revert">Use revert instead of require </a> </li> <li> <a href="#memory">Avoid loading too many data in memory</a> </li> <li> <a href="#tips">Other tips</a> </li> </ul> <h2> <a name="use-constant-and-immutable-variables-for-variable-that-dont-change" href="#use-constant-and-immutable-variables-for-variable-that-dont-change"> </a> <a name="constant"></a> Use constant and immutable variables for variable that don't change </h2> <p>Using the <code>constant</code> and the <code>immutable</code> keywords for variables that do not change helps to save on <code>gas</code> used. The reason been that <code>constant</code> and <code>immutable</code> variables do not occupy a storage slot when compiled. They are saved inside the contract byte code. Lets see an example.<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code><span class="c1">//SPDX-License-Identifier:MIT</span> <span class="nx">pragma</span> <span class="nx">solidity</span> <span class="o">^</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">3</span><span class="p">;</span> <span class="kr">interface</span> <span class="nx">IERC20</span> <span class="p">{</span> <span class="kd">function</span> <span class="nx">transfer</span><span class="p">(</span><span class="nx">address</span> <span class="nx">to</span><span class="p">,</span> <span class="nx">uint256</span> <span class="nx">value</span><span class="p">)</span> <span class="nx">external</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">bool</span><span class="p">);</span> <span class="kd">function</span> <span class="nx">approve</span><span class="p">(</span><span class="nx">address</span> <span class="nx">spender</span><span class="p">,</span> <span class="nx">uint256</span> <span class="nx">value</span><span class="p">)</span> <span class="nx">external</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">bool</span><span class="p">);</span> <span class="kd">function</span> <span class="nx">transferFrom</span><span class="p">(</span><span class="nx">address</span> <span class="k">from</span><span class="p">,</span> <span class="nx">address</span> <span class="nx">to</span><span class="p">,</span> <span class="nx">uint256</span> <span class="nx">value</span><span class="p">)</span> <span class="nx">external</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">bool</span><span class="p">);</span> <span class="c1">//rest of the interface code</span> <span class="p">}</span> <span class="c1">//Gas used: 187302</span> <span class="nx">contract</span> <span class="nx">Expensive</span> <span class="p">{</span> <span class="nx">IERC20</span> <span class="kr">public</span> <span class="nx">token</span><span class="p">;</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">timeStamp</span> <span class="o">=</span> <span class="mi">566777</span><span class="p">;</span> <span class="kd">constructor</span><span class="p">(</span><span class="nx">address</span> <span class="nx">token_address</span><span class="p">)</span> <span class="p">{</span> <span class="nx">token</span> <span class="o">=</span> <span class="nx">IERC20</span><span class="p">();</span> <span class="p">}</span> <span class="p">}</span> <span class="c1">//Gas used: 142890</span> <span class="nx">contract</span> <span class="nx">GasSaver</span> <span class="p">{</span> <span class="nx">IERC20</span> <span class="kr">public</span> <span class="nx">immutable</span> <span class="nx">i_token</span><span class="p">;</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">constant</span> <span class="nx">TIMESTAMP</span> <span class="o">=</span> <span class="mi">566777</span><span class="p">;</span> <span class="kd">constructor</span><span class="p">(</span><span class="nx">address</span> <span class="nx">token_address</span><span class="p">)</span> <span class="p">{</span> <span class="nx">i_token</span> <span class="o">=</span> <span class="nx">IERC20</span><span class="p">(</span><span class="nx">token_address</span><span class="p">);</span> <span class="p">}</span> <span class="p">}</span> </code></pre> <div class="highlight__panel js-actions-panel"> <div class="highlight__panel-action js-fullscreen-code-action"> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-on"><title>Enter fullscreen mode</title> <path d="M16 3h6v6h-2V5h-4V3zM2 3h6v2H4v4H2V3zm18 16v-4h2v6h-6v-2h4zM4 19h4v2H2v-6h2v4z"></path> </svg> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-off"><title>Exit fullscreen mode</title> <path d="M18 7h4v2h-6V3h2v4zM8 9H2V7h4V3h2v6zm10 8v4h-2v-6h6v2h-4zM8 15v6H6v-4H2v-2h6z"></path> </svg> </div> </div> </div> <p>The first contract <code>Expensive</code> has a public variable of type <code>IERC20</code> and a <code>uint256</code> also defined as public. When we deployed this contract, the contract deployment used up a total of 187302 <code>gas</code> when deployed to Remix. The second contract named <code>GasSaver</code> also have the same variable structure as the <code>Expensive</code> contract but we made use of <code>constant</code> keyword for the <code>TIMESTAMP</code> because we will not be changing the value. For the <code>interface</code> we used the <code>immutable</code> keyword which means we can no longer modify the value of the <code>i_token</code> variable after setting it inside the <code>constructor</code>. This action alone reduced the gas consumption from 187302 to 142890.</p> <h2> <a name="cache-read-variables-in-memory" href="#cache-read-variables-in-memory"> </a> <a name="constant"></a> Cache read variables in memory </h2> <p>Reading from a variable in storage cost <code>gas</code>. When we access a variable for the first time it cost <code>2100 gas</code> and subsequent access will cost <code>100 gas</code>. If we have an array and want to perform some computation on the array elements. It could be more gas effective to read the <code>length</code> of the array and store it in a variable. If the array is not too large we could also read the whole <code>array</code> into memory and access it from memory instead of continuously reading from storage.<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code> <span class="c1">//SPDX-License-Identifier:MIT;</span> <span class="nx">pragma</span> <span class="nx">solidity</span> <span class="o">^</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">3</span><span class="p">;</span> <span class="nx">contract</span> <span class="nx">Expensive</span> <span class="p">{</span> <span class="nx">uint256</span><span class="p">[]</span> <span class="kr">public</span> <span class="nx">numbers</span><span class="p">;</span> <span class="kd">constructor</span><span class="p">(</span><span class="nx">uint256</span><span class="p">[]</span> <span class="nx">memory</span> <span class="nx">_numbers</span><span class="p">)</span> <span class="p">{</span> <span class="nx">numbers</span> <span class="o">=</span> <span class="nx">_numbers</span><span class="p">;</span> <span class="p">}</span> <span class="c1">//Gas used: 40146</span> <span class="kd">function</span> <span class="nx">sum</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">view</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">uint256</span> <span class="p">){</span> <span class="nx">uint256</span> <span class="nx">total</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="k">for</span> <span class="p">(</span><span class="nx">uint256</span> <span class="nx">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="o"><</span> <span class="nx">numbers</span><span class="p">.</span><span class="nx">length</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span> <span class="nx">total</span> <span class="o">+=</span> <span class="nx">numbers</span><span class="p">[</span><span class="nx">i</span><span class="p">];</span> <span class="p">}</span> <span class="k">return</span> <span class="nx">total</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> <span class="nx">contract</span> <span class="nx">GasSaver</span> <span class="p">{</span> <span class="nx">uint256</span><span class="p">[]</span> <span class="kr">public</span> <span class="nx">numbers</span><span class="p">;</span> <span class="kd">constructor</span><span class="p">(</span><span class="nx">uint256</span><span class="p">[]</span> <span class="nx">memory</span> <span class="nx">_numbers</span><span class="p">)</span> <span class="p">{</span> <span class="nx">numbers</span> <span class="o">=</span> <span class="nx">_numbers</span><span class="p">;</span> <span class="p">}</span> <span class="c1">//39434</span> <span class="kd">function</span> <span class="nx">sum</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">view</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">uint256</span> <span class="p">){</span> <span class="nx">uint256</span> <span class="nx">total</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">uint256</span> <span class="nx">arrLength</span> <span class="o">=</span> <span class="nx">numbers</span><span class="p">.</span><span class="nx">length</span><span class="p">;</span> <span class="nx">uint256</span><span class="p">[]</span> <span class="nx">memory</span> <span class="nx">_numbersInMemory</span> <span class="o">=</span> <span class="nx">numbers</span><span class="p">;</span> <span class="k">for</span> <span class="p">(</span><span class="nx">uint256</span> <span class="nx">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="o"><</span> <span class="nx">arrLength</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span> <span class="nx">total</span> <span class="o">+=</span> <span class="nx">_numbersInMemory</span><span class="p">[</span><span class="nx">i</span><span class="p">];</span> <span class="p">}</span> <span class="k">return</span> <span class="nx">total</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> </code></pre> <div class="highlight__panel js-actions-panel"> <div class="highlight__panel-action js-fullscreen-code-action"> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-on"><title>Enter fullscreen mode</title> <path d="M16 3h6v6h-2V5h-4V3zM2 3h6v2H4v4H2V3zm18 16v-4h2v6h-6v-2h4zM4 19h4v2H2v-6h2v4z"></path> </svg> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-off"><title>Exit fullscreen mode</title> <path d="M18 7h4v2h-6V3h2v4zM8 9H2V7h4V3h2v6zm10 8v4h-2v-6h6v2h-4zM8 15v6H6v-4H2v-2h6z"></path> </svg> </div> </div> </div> <p>The contract <code>GasSaver</code> above saved the length of the array in a variable <code>arrLength</code> and also loaded the array into memory. This helps to reduce the <code>gas</code> spent inside the function.</p> <h2> <a name="incrementing-and-decrementing-by-1" href="#incrementing-and-decrementing-by-1"> </a> <a name="incrementing"></a> Incrementing and Decrementing by 1 </h2> <p>There are four ways to increment and decrement a variable by 1 in Solidity. Let us see an example.<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code><span class="c1">//SPDX-License-Identifier:MIT;</span> <span class="nx">pragma</span> <span class="nx">solidity</span> <span class="o">^</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">3</span><span class="p">;</span> <span class="nx">contract</span> <span class="nx">One</span><span class="p">{</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">number</span><span class="p">;</span> <span class="c1">//Gas used : 43800</span> <span class="kd">function</span> <span class="nx">incrementByOne</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">uint256</span><span class="p">){</span> <span class="nx">number</span> <span class="o">+=</span> <span class="mi">1</span><span class="p">;</span> <span class="k">return</span> <span class="nx">number</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> <span class="nx">contract</span> <span class="nx">Two</span><span class="p">{</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">number</span><span class="p">;</span> <span class="c1">//Gas used : 43787</span> <span class="kd">function</span> <span class="nx">incrementByOne</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">uint256</span><span class="p">){</span> <span class="nx">number</span> <span class="o">=</span> <span class="nx">number</span> <span class="o">+</span> <span class="mi">1</span><span class="p">;</span> <span class="k">return</span> <span class="nx">number</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> <span class="nx">contract</span> <span class="nx">Three</span><span class="p">{</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">number</span><span class="p">;</span> <span class="c1">//Gas used : 43634</span> <span class="kd">function</span> <span class="nx">incrementByOne</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">uint256</span><span class="p">){</span> <span class="k">return</span> <span class="nx">number</span><span class="o">++</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> <span class="nx">contract</span> <span class="nx">Four</span><span class="p">{</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">number</span><span class="p">;</span> <span class="c1">//Gas used : 43628</span> <span class="kd">function</span> <span class="nx">incrementByOne</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">uint256</span><span class="p">){</span> <span class="k">return</span> <span class="o">++</span><span class="nx">number</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> </code></pre> <div class="highlight__panel js-actions-panel"> <div class="highlight__panel-action js-fullscreen-code-action"> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-on"><title>Enter fullscreen mode</title> <path d="M16 3h6v6h-2V5h-4V3zM2 3h6v2H4v4H2V3zm18 16v-4h2v6h-6v-2h4zM4 19h4v2H2v-6h2v4z"></path> </svg> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-off"><title>Exit fullscreen mode</title> <path d="M18 7h4v2h-6V3h2v4zM8 9H2V7h4V3h2v6zm10 8v4h-2v-6h6v2h-4zM8 15v6H6v-4H2v-2h6z"></path> </svg> </div> </div> </div> <p>The example above list four contracts which shows the way we could increment a number variable by a value of 1. The contract <code>Four</code> is more gas effective out of the lot when ran. To save more on <code>gas</code> when incrementing a variable use the method of increment in contract <code>Four</code> (<code>++number</code>) which is more <code>gas</code> efficient.</p> <h2> <a name="calldata-and-memory" href="#calldata-and-memory"> </a> <a name="calldata"></a> calldata and memory </h2> <p>When running a function we could pass the function parameters as <code>calldata</code> or <code>memory</code> for variables such as <code>strings</code>, <code>structs</code>,<code>arrays</code> etc. If we are not modifying the passed parameter we should pass it as <code>calldata</code> because <code>calldata</code> is more <code>gas</code> efficient than <code>memory</code>. Let's see an example:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code><span class="c1">//SPDX-License-Identifier:MIT;</span> <span class="nx">pragma</span> <span class="nx">solidity</span> <span class="o">^</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">3</span><span class="p">;</span> <span class="nx">contract</span> <span class="nx">GasSaver</span> <span class="p">{</span> <span class="c1">//Gas used: 22471</span> <span class="kd">function</span> <span class="nx">passParameterAsCallData</span><span class="p">(</span><span class="nx">string</span> <span class="nx">calldata</span> <span class="nx">_name</span><span class="p">)</span> <span class="kr">public</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">string</span> <span class="nx">memory</span><span class="p">){}</span> <span class="c1">//Gas used: 22913</span> <span class="kd">function</span> <span class="nx">passParameterAsMemory</span><span class="p">(</span><span class="nx">string</span> <span class="nx">memory</span> <span class="nx">_name</span><span class="p">)</span> <span class="kr">public</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">string</span> <span class="nx">memory</span><span class="p">){}</span> <span class="p">}</span> </code></pre> <div class="highlight__panel js-actions-panel"> <div class="highlight__panel-action js-fullscreen-code-action"> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-on"><title>Enter fullscreen mode</title> <path d="M16 3h6v6h-2V5h-4V3zM2 3h6v2H4v4H2V3zm18 16v-4h2v6h-6v-2h4zM4 19h4v2H2v-6h2v4z"></path> </svg> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-off"><title>Exit fullscreen mode</title> <path d="M18 7h4v2h-6V3h2v4zM8 9H2V7h4V3h2v6zm10 8v4h-2v-6h6v2h-4zM8 15v6H6v-4H2v-2h6z"></path> </svg> </div> </div> </div> <p>Calling these two functions in Remix and passing the same parameter to the functions, you will noticed that setting a function <code>_name</code> parameter as <code>calldata</code> reduced the <code>gas</code> used. </p> <blockquote> <p>You can only used <code>calldata</code> when you are not going to modify the value of the variable passed as <code>calldata</code> inside the function.</p> </blockquote> <h2> <a name="calling-a-raw-view-endraw-function" href="#calling-a-raw-view-endraw-function"> </a> <a name="view"></a> Calling a <code>view</code> function </h2> <p>A <code>view</code> function does not use <code>gas</code> when called, but if we decide to call a view function inside of another function which is a transaction, it then uses <code>gas</code>.<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code><span class="c1">//SPDX-License-Identifier:MIT;</span> <span class="nx">pragma</span> <span class="nx">solidity</span> <span class="o">^</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">3</span><span class="p">;</span> <span class="nx">contract</span> <span class="nx">GasSaver</span> <span class="p">{</span> <span class="nx">uint256</span><span class="p">[]</span> <span class="kr">private</span> <span class="nx">numbers</span> <span class="o">=</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">67</span><span class="p">,</span><span class="mi">34</span><span class="p">];</span> <span class="kd">function</span> <span class="nx">getNumberAt</span><span class="p">(</span> <span class="nx">uint256</span> <span class="nx">_index</span> <span class="p">)</span> <span class="kr">public</span> <span class="nx">view</span> <span class="nx">returns</span> <span class="p">(</span><span class="nx">uint256</span><span class="p">){</span> <span class="k">return</span> <span class="nx">numbers</span><span class="p">[</span><span class="nx">_index</span><span class="p">];</span> <span class="p">}</span> <span class="c1">//Gas used when getNumber was called: 44778</span> <span class="c1">//Gas used without calling getNumber() 44450</span> <span class="kd">function</span> <span class="nx">sumAndMultiply</span><span class="p">()</span> <span class="kr">public</span> <span class="p">{</span> <span class="nx">uint256</span><span class="p">[]</span> <span class="nx">memory</span> <span class="nx">_numbers</span> <span class="o">=</span> <span class="nx">numbers</span><span class="p">;</span> <span class="nx">uint256</span> <span class="nx">arrlength</span> <span class="o">=</span> <span class="nx">_numbers</span><span class="p">.</span><span class="nx">length</span><span class="p">;</span> <span class="k">for</span><span class="p">(</span><span class="nx">uint256</span> <span class="nx">i</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="o"><</span> <span class="nx">arrlength</span><span class="p">;</span> <span class="o">++</span><span class="nx">i</span><span class="p">){</span> <span class="nx">numbers</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span> <span class="o">=</span> <span class="nx">_numbers</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span> <span class="o">*</span> <span class="nx">i</span><span class="p">;</span> <span class="p">}</span> <span class="c1">//getNumberAt(2);</span> <span class="p">}</span> <span class="p">}</span> </code></pre> <div class="highlight__panel js-actions-panel"> <div class="highlight__panel-action js-fullscreen-code-action"> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-on"><title>Enter fullscreen mode</title> <path d="M16 3h6v6h-2V5h-4V3zM2 3h6v2H4v4H2V3zm18 16v-4h2v6h-6v-2h4zM4 19h4v2H2v-6h2v4z"></path> </svg> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-off"><title>Exit fullscreen mode</title> <path d="M18 7h4v2h-6V3h2v4zM8 9H2V7h4V3h2v6zm10 8v4h-2v-6h6v2h-4zM8 15v6H6v-4H2v-2h6z"></path> </svg> </div> </div> </div> <p>The above is a simple contract to illustrate the point about calling <code>view</code> functions inside of a transaction. The function <code>getNumberAt</code> is a <code>view</code> function that returns the value of the array at the passed index. Calling this function uses no <code>gas</code> because it is a view function, but if we decide to call this function inside of the <code>sumAndMultiply</code> function, we can see that the <code>gas</code> usage of <code>sumAndMultiply</code> <br> has increased because the <code>view</code> function is called within it.</p> <p><code>Gas</code> used when <code>sumAndMutiply</code> functions is called: <code>44778</code>.<br> <code>Gas</code> used when <code>getNumberAt</code> <code>view</code> function is also called inside the <code>sumAndMultiply</code> function: <code>44450</code>.</p> <p>So, we can see that calling a <code>view</code> function inside a transaction increased the amount of <code>gas</code> that should have been spent, if the <code>view</code> function was not included in the call.</p> <h2> <a name="integer-overflowunderflow" href="#integer-overflowunderflow"> </a> <a name="overflow"></a> Integer overflow/underflow </h2> <p>Prior to Solidity <code>0.8.0</code> version, interger overflow and underflow checks were performed by using the <code>SafeMath</code> library. From Solidity <code>0.8.0</code> upward, the compiler does that check for us. </p> <p>This extra check cost <code>gas</code>. If we know that the mathematical operations we will perform inside the contract will not overflow or underflow, we can tell the compiler not to check for overflow or underflow in the operation.<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code><span class="c1">//SPDX-License-Identifier:MIT;</span> <span class="nx">pragma</span> <span class="nx">solidity</span> <span class="o">^</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">3</span><span class="p">;</span> <span class="nx">contract</span> <span class="nx">OverFlow</span> <span class="p">{</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">numberOne</span><span class="p">;</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">numberTwo</span><span class="p">;</span> <span class="c1">//Gas used: 43440</span> <span class="kd">function</span> <span class="nx">setNumberOne</span><span class="p">()</span> <span class="kr">public</span> <span class="p">{</span> <span class="o">++</span><span class="nx">numberOne</span><span class="p">;</span> <span class="p">}</span> <span class="c1">//Gas used: 43339</span> <span class="kd">function</span> <span class="nx">setNumberTwo</span><span class="p">()</span> <span class="kr">public</span> <span class="p">{</span> <span class="nx">unchecked</span> <span class="p">{</span> <span class="o">++</span><span class="nx">numberTwo</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> <span class="p">}</span> </code></pre> <div class="highlight__panel js-actions-panel"> <div class="highlight__panel-action js-fullscreen-code-action"> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-on"><title>Enter fullscreen mode</title> <path d="M16 3h6v6h-2V5h-4V3zM2 3h6v2H4v4H2V3zm18 16v-4h2v6h-6v-2h4zM4 19h4v2H2v-6h2v4z"></path> </svg> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-off"><title>Exit fullscreen mode</title> <path d="M18 7h4v2h-6V3h2v4zM8 9H2V7h4V3h2v6zm10 8v4h-2v-6h6v2h-4zM8 15v6H6v-4H2v-2h6z"></path> </svg> </div> </div> </div> <p>The above contract <code>OverFlow</code> has two functions used to set two variables inside the contract. The compiler in <code>setNumberOne</code> checks and prevents the number from overflow or underflow. In the second function <code>setNumberTwo</code> we are telling the compiler to mind its business and not check for overflow or underflow. Using <code>unchecked</code> means that the code block will not be checked for overflow or underflow.</p> <p>If we know that our mathematics will be safe we could safe a little gas by using <code>unchecked</code>.</p> <h2> <a name="use-revert-instead-of-require" href="#use-revert-instead-of-require"> </a> <a name="revert"></a> Use revert instead of require </h2> <p>We use <code>require</code> to check if a statement is <code>true</code>. If the statement evaluates to false the transaction is reverted and the remaining gas returned to the user. Since the advert of custom error in Solidity we could use the <code>revert</code> statement to throw a custom error. Using <code>revert</code> instead of <code>require</code> is more gas efficient. You can run the code below to see the the amount of <code>gas</code> saved when <code>revert</code> is used instead of <code>require</code>.<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code><span class="c1">//SPDX-License-Identifier:MIT;</span> <span class="nx">pragma</span> <span class="nx">solidity</span> <span class="o">^</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">3</span><span class="p">;</span> <span class="nx">error</span> <span class="nx">NotEnough</span><span class="p">();</span> <span class="nx">contract</span> <span class="nx">GasSaver</span> <span class="p">{</span> <span class="nx">uint256</span> <span class="kr">public</span> <span class="nx">number</span><span class="p">;</span> <span class="c1">//Gas Used: 21898</span> <span class="kd">function</span> <span class="nx">setNumber</span><span class="p">(</span><span class="nx">uint256</span> <span class="nx">_number</span><span class="p">)</span> <span class="kr">public</span> <span class="p">{</span> <span class="nx">require</span><span class="p">(</span><span class="nx">_number</span> <span class="o">></span> <span class="mi">10</span><span class="p">,</span> <span class="dl">"</span><span class="s2">number too small please</span><span class="dl">"</span><span class="p">);</span> <span class="nx">number</span> <span class="o">=</span> <span class="nx">_number</span><span class="p">;</span> <span class="p">}</span> <span class="c1">//Gas Used: 21669</span> <span class="kd">function</span> <span class="nx">setNumberAndRevert</span><span class="p">(</span><span class="nx">uint256</span> <span class="nx">_number</span><span class="p">)</span> <span class="kr">public</span> <span class="p">{</span> <span class="k">if</span> <span class="p">(</span> <span class="nx">_number</span> <span class="o"><</span> <span class="mi">10</span> <span class="p">){</span> <span class="nx">revert</span> <span class="nx">NotEnough</span><span class="p">();</span> <span class="p">}</span> <span class="nx">number</span> <span class="o">=</span> <span class="nx">_number</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> </code></pre> <div class="highlight__panel js-actions-panel"> <div class="highlight__panel-action js-fullscreen-code-action"> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-on"><title>Enter fullscreen mode</title> <path d="M16 3h6v6h-2V5h-4V3zM2 3h6v2H4v4H2V3zm18 16v-4h2v6h-6v-2h4zM4 19h4v2H2v-6h2v4z"></path> </svg> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-off"><title>Exit fullscreen mode</title> <path d="M18 7h4v2h-6V3h2v4zM8 9H2V7h4V3h2v6zm10 8v4h-2v-6h6v2h-4zM8 15v6H6v-4H2v-2h6z"></path> </svg> </div> </div> </div> <h2> <a name="avoid-loading-too-many-data-in-memory" href="#avoid-loading-too-many-data-in-memory"> </a> <a name="memory"></a> Avoid loading too many data in memory </h2> <p>Loading data in memory in a single transaction has the effect of increasing <code>gas</code>used. The <code>gas</code> used increase in a quadratic factor when more than <code>32kb</code> of memory is used in a single transaction. Let's see an example.<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code><span class="c1">//SPDX-License-Identifier:MIT;</span> <span class="nx">pragma</span> <span class="nx">solidity</span> <span class="o">^</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">3</span><span class="p">;</span> <span class="nx">contract</span> <span class="nx">One</span> <span class="p">{</span> <span class="c1">//Gas used: 29261</span> <span class="kd">function</span> <span class="nx">setArrayInMemory</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">pure</span> <span class="p">{</span> <span class="nx">uint256</span><span class="p">[</span><span class="mi">1000</span><span class="p">]</span> <span class="nx">memory</span> <span class="nx">_array</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> <span class="nx">contract</span> <span class="nx">Two</span> <span class="p">{</span> <span class="c1">//Gas used: 276761</span> <span class="kd">function</span> <span class="nx">setArrayInMemory</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">pure</span> <span class="p">{</span> <span class="nx">uint256</span><span class="p">[</span><span class="mi">10000</span><span class="p">]</span> <span class="nx">memory</span> <span class="nx">_array</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> <span class="c1">//Gas used: 922855</span> <span class="nx">contract</span> <span class="nx">Three</span> <span class="p">{</span> <span class="kd">function</span> <span class="nx">setArrayInMemory</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">pure</span> <span class="p">{</span> <span class="nx">uint256</span><span class="p">[</span><span class="mi">20000</span><span class="p">]</span> <span class="nx">memory</span> <span class="nx">_array</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> <span class="nx">contract</span> <span class="nx">Four</span> <span class="p">{</span> <span class="c1">//Gas used: 3386918</span> <span class="kd">function</span> <span class="nx">setArrayInMemory</span><span class="p">()</span> <span class="kr">public</span> <span class="nx">pure</span> <span class="p">{</span> <span class="nx">uint256</span><span class="p">[</span><span class="mi">40000</span><span class="p">]</span> <span class="nx">memory</span> <span class="nx">_array</span><span class="p">;</span> <span class="p">}</span> <span class="p">}</span> </code></pre> <div class="highlight__panel js-actions-panel"> <div class="highlight__panel-action js-fullscreen-code-action"> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-on"><title>Enter fullscreen mode</title> <path d="M16 3h6v6h-2V5h-4V3zM2 3h6v2H4v4H2V3zm18 16v-4h2v6h-6v-2h4zM4 19h4v2H2v-6h2v4z"></path> </svg> <svg xmlns="http://www.w3.org/2000/svg" width="20px" height="20px" viewbox="0 0 24 24" class="highlight-action crayons-icon highlight-action--fullscreen-off"><title>Exit fullscreen mode</title> <path d="M18 7h4v2h-6V3h2v4zM8 9H2V7h4V3h2v6zm10 8v4h-2v-6h6v2h-4zM8 15v6H6v-4H2v-2h6z"></path> </svg> </div> </div> </div> <p>The above example defined four contracts and each contract has a function named <code>setArrayInMemory</code> where memory space is reserved for an array of <code>uint256</code>. </p> <p>Contract <code>One</code> loads reserves space in memory for 1000 <code>uint256</code> numbers and when the function is executed it uses up 29261 <code>gas</code>. Contract <code>Two</code> creates memory space for 10000 <code>uint256</code> numbers and we can see that the <code>gas</code> used is 276761 which is roughly about 10 times of the <code>gas</code> used by Contract <code>One</code>.</p> <p>Things gets interesting in Contract <code>Three</code> which reserves space for 20000 <code>uint256</code> numbers. From the <code>gas</code> used which is 922855, we can see that once the memory used in a single transaction exceeds 32 kilobyte, the quadratic factor of the memory expansion cost kicks in thereby increasing the <code>gas</code> used in a quadratic way.</p> <blockquote> <p>Do not populate arrays with enormous amounts of items in a single transaction to prevent <code>gas</code> used increase in a quadratic way.</p> </blockquote> <h2> <a name="other-tips" href="#other-tips"> </a> <a name="tips"></a> Other tips </h2> <ul> <li><p>Always put your <code>require</code> statement on top in the function before making any state change so that if the <code>require</code> statement fails, the remaining <code>gas</code> is refunded to the user on revert.</p></li> <li><p>When comparing operation using <code>&&</code> or <code>||</code> with a <code>require</code> statement; you should put the cheaper part of the operation first so that if it fails, the compiler will not compare the second part thereby saving on <code>gas</code> used.</p></li> </ul> <p>In conclusion We can use a combination of these techniques highlighted here to improve the <code>gas</code> consumption of our smart contracts thereby saving our users from spending too much on <code>gas</code> when interacting with our smart contracts.</p> <p>Thanks for reading.</p> </div> <div class="js-billboard-container body-billboard-container" data-async-url="/jamiescript/gas-saving-techniques-in-solidity-324c/billboards/post_body_bottom"></div> </div> <section id="comments" data-follow-button-container="true" data-updated-at="2025-01-05 22:25:31 UTC" class="text-padding mb-4 border-t-1 border-0 border-solid border-base-10"> <header class="relative flex justify-between items-center mb-6"> <div class="flex items-center"> <h2 class="crayons-subtitle-1"> Top comments <span class="js-comments-count" data-comments-count="0">(0)</span> </h2> </div> <div id="comment-subscription" class="print-hidden"> <div 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<li> <div class="key"> Location </div> <div class="value"> Uyo, Nigeria </div> </li> <li> <div class="key"> Education </div> <div class="value"> University of Ilorin </div> </li> <li> <div class="key"> Work </div> <div class="value"> Author @ Educative.io </div> </li> <li> <div class="key"> Joined </div> <div class="value"> <time datetime="2020-03-22T13:16:17Z" class="date">Mar 22, 2020</time> </div> </li> </ul> </div> </div> <div class="crayons-card crayons-card--secondary"> <header class="crayons-card__header"> <h3 class="crayons-subtitle-2"> More from <a href="/jamiescript">Jamiebones</a> </h3> </header> <div> <a class="crayons-link crayons-link--contentful" href="/jamiescript/how-to-create-and-deploy-an-nft-smart-contract-2gj8"> How to Create and Deploy an NFT Smart Contract <div class="crayons-link__secondary -ml-1"> <span class="mr-1"><span class="opacity-50">#</span>solidity</span> <span class="mr-1"><span class="opacity-50">#</span>nft</span> <span class="mr-1"><span 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