library/index.html

<!DOCTYPE html><html class="fa-events-icons-ready" lang="en"><head><meta charset="utf-8"><link href="/favicon.ico" rel="shortcut icon"><meta content="width=device-width,initial-scale=1,shrink-to-fit=yes" name="viewport"><meta content="#000000" name="theme-color"><script src="https://www.google-analytics.com/analytics.js" async type="text/javascript"></script><script src="https://use.fontawesome.com/ba3dde78ee.js"></script><link href="https://www.googletagmanager.com" rel="preconnect"><link href="https://use.fontawesome.com/ba3dde78ee.css" rel="stylesheet" media="all"><link href="/manifest.json" rel="manifest"><title>Library | Solidity by Example | 0.7.6</title><script src="https://www.googletagmanager.com/gtag/js?id=UA-133759045-1" async></script><script>function gtag(){dataLayer.push(arguments)}window.dataLayer=window.dataLayer||[],gtag("js",new Date),gtag("config","UA-133759045-1")</script><link href="/static/css/2.8a5f298e.chunk.css" rel="stylesheet"><link href="/static/css/main.b19412ac.chunk.css" rel="stylesheet"><link href="https://use.fontawesome.com" rel="preconnect"><meta content="Example of how to write and use libraries in your Solidity code" name="Description" data-react-helmet="true"><link href="https://www.google-analytics.com" rel="preconnect"></head><body><noscript>You need to enable JavaScript to run this app.</noscript><div id="root"><div class="App_component__1dd61"><div class="Header_component__1tkkW"><a href="/"><img alt="logo" class="Header_logo__2ins2" src="/static/media/logo.9a07f18c.svg"></a><h3 class="Header_header__3mObx"><a href="/">Solidity by Example</a><div class="Header_versions__eOBao"><div class="Header_version__1QJXf">version 0.7.6</div></div></h3></div><div class="App_main__3ZkGI"><div class="Example_component__mzuGC"><div class="Example_content__3-AiU"><h2>Library</h2><div><p>Libraries are similar to contracts, but you can't declare any state variable and you can't send ether.</p><p>A library is embedded into the contract if all library functions are internal.</p><p>Otherwise the library must be deployed and then linked before the contract is deployed.</p><pre><code class="language-solidity"><span class="hljs-comment">// SPDX-License-Identifier: MIT</span>
<span class="hljs-meta"><span class="hljs-keyword">pragma</span> <span class="hljs-keyword">solidity</span> ^0.7.6;</span>

<span class="hljs-class"><span class="hljs-keyword">library</span> <span class="hljs-title">SafeMath</span> </span>{
    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">add</span>(<span class="hljs-params"><span class="hljs-keyword">uint</span> x, <span class="hljs-keyword">uint</span> y</span>) <span class="hljs-title"><span class="hljs-keyword">internal</span></span> <span class="hljs-title"><span class="hljs-keyword">pure</span></span> <span class="hljs-title"><span class="hljs-keyword">returns</span></span> (<span class="hljs-params"><span class="hljs-keyword">uint</span></span>) </span>{
        <span class="hljs-keyword">uint</span> z = x + y;
        <span class="hljs-built_in">require</span>(z >= x, <span class="hljs-string">"uint overflow"</span>);

        <span class="hljs-keyword">return</span> z;
    }
}

<span class="hljs-class"><span class="hljs-keyword">contract</span> <span class="hljs-title">TestSafeMath</span> </span>{
    <span class="hljs-keyword">using</span> <span class="hljs-title">SafeMath</span> <span class="hljs-title"><span class="hljs-keyword">for</span></span> <span class="hljs-title"><span class="hljs-keyword">uint</span></span>;

    <span class="hljs-keyword">uint</span> <span class="hljs-keyword">public</span> MAX_UINT = <span class="hljs-number">2</span> ** <span class="hljs-number">256</span> - <span class="hljs-number">1</span>;

    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">testAdd</span>(<span class="hljs-params"><span class="hljs-keyword">uint</span> x, <span class="hljs-keyword">uint</span> y</span>) <span class="hljs-title"><span class="hljs-keyword">public</span></span> <span class="hljs-title"><span class="hljs-keyword">pure</span></span> <span class="hljs-title"><span class="hljs-keyword">returns</span></span> (<span class="hljs-params"><span class="hljs-keyword">uint</span></span>) </span>{
        <span class="hljs-keyword">return</span> x.add(y);
    }
}

<span class="hljs-comment">// Array function to delete element at index and re-organize the array</span>
<span class="hljs-comment">// so that their are no gaps between the elements.</span>
<span class="hljs-class"><span class="hljs-keyword">library</span> <span class="hljs-title">Array</span> </span>{
    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">remove</span>(<span class="hljs-params"><span class="hljs-keyword">uint</span>[] <span class="hljs-keyword">storage</span> arr, <span class="hljs-keyword">uint</span> index</span>) <span class="hljs-title"><span class="hljs-keyword">public</span></span> </span>{
        <span class="hljs-comment">// Move the last element into the place to delete</span>
        arr[index] = arr[arr.<span class="hljs-built_in">length</span> - <span class="hljs-number">1</span>];
        arr.<span class="hljs-built_in">pop</span>();
    }
}

<span class="hljs-class"><span class="hljs-keyword">contract</span> <span class="hljs-title">TestArray</span> </span>{
    <span class="hljs-keyword">using</span> <span class="hljs-title">Array</span> <span class="hljs-title"><span class="hljs-keyword">for</span></span> <span class="hljs-title"><span class="hljs-keyword">uint</span></span>[];

    <span class="hljs-keyword">uint</span>[] <span class="hljs-keyword">public</span> arr;

    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">testArrayRemove</span>(<span class="hljs-params"></span>) <span class="hljs-title"><span class="hljs-keyword">public</span></span> </span>{
        <span class="hljs-keyword">for</span> (<span class="hljs-keyword">uint</span> i = <span class="hljs-number">0</span>; i &lt; <span class="hljs-number">3</span>; i++) {
            arr.<span class="hljs-built_in">push</span>(i);
        }

        arr.remove(<span class="hljs-number">1</span>);

        <span class="hljs-built_in">assert</span>(arr.<span class="hljs-built_in">length</span> == <span class="hljs-number">2</span>);
        <span class="hljs-built_in">assert</span>(arr[<span class="hljs-number">0</span>] == <span class="hljs-number">0</span>);
        <span class="hljs-built_in">assert</span>(arr[<span class="hljs-number">1</span>] == <span class="hljs-number">2</span>);
    }
}
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