interface/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>Interface | 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"><link href="https://www.google-analytics.com" rel="preconnect"><meta content="An example of interface in Solidity" name="Description" data-react-helmet="true"></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>Interface</h2><div><p>You can interact with other contracts by declaring an <code>Interface</code>.</p><p>Interface</p><ul><li>cannot have any functions implemented</li><li>can inherit from other interfaces</li><li>all declared functions must be external</li><li>cannot declare a constructor</li><li>cannot declare state variables</li></ul><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">contract</span> <span class="hljs-title">Counter</span> </span>{
    <span class="hljs-keyword">uint</span> <span class="hljs-keyword">public</span> count;

    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">increment</span>(<span class="hljs-params"></span>) <span class="hljs-title"><span class="hljs-keyword">external</span></span> </span>{
        count += <span class="hljs-number">1</span>;
    }
}

<span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">ICounter</span> </span>{
    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">count</span>(<span class="hljs-params"></span>) <span class="hljs-title"><span class="hljs-keyword">external</span></span> <span class="hljs-title"><span class="hljs-keyword">view</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-function"><span class="hljs-keyword">function</span> <span class="hljs-title">increment</span>(<span class="hljs-params"></span>) <span class="hljs-title"><span class="hljs-keyword">external</span></span></span>;
}

<span class="hljs-class"><span class="hljs-keyword">contract</span> <span class="hljs-title">MyContract</span> </span>{
    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">incrementCounter</span>(<span class="hljs-params"><span class="hljs-keyword">address</span> _counter</span>) <span class="hljs-title"><span class="hljs-keyword">external</span></span> </span>{
        ICounter(_counter).increment();
    }

    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">getCount</span>(<span class="hljs-params"><span class="hljs-keyword">address</span> _counter</span>) <span class="hljs-title"><span class="hljs-keyword">external</span></span> <span class="hljs-title"><span class="hljs-keyword">view</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> ICounter(_counter).count();
    }
}

<span class="hljs-comment">// Uniswap example</span>
<span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">UniswapV2Factory</span> </span>{
    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">getPair</span>(<span class="hljs-params"><span class="hljs-keyword">address</span> tokenA, <span class="hljs-keyword">address</span> tokenB</span>) <span class="hljs-title"><span class="hljs-keyword">external</span></span> <span class="hljs-title"><span class="hljs-keyword">view</span></span> <span class="hljs-title"><span class="hljs-keyword">returns</span></span> (<span class="hljs-params"><span class="hljs-keyword">address</span> pair</span>)</span>;
}

<span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">UniswapV2Pair</span> </span>{
    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">getReserves</span>(<span class="hljs-params"></span>) <span class="hljs-title"><span class="hljs-keyword">external</span></span> <span class="hljs-title"><span class="hljs-keyword">view</span></span> <span class="hljs-title"><span class="hljs-keyword">returns</span></span> (<span class="hljs-params"><span class="hljs-keyword">uint112</span> reserve0, <span class="hljs-keyword">uint112</span> reserve1, <span class="hljs-keyword">uint32</span> blockTimestampLast</span>)</span>;
}

<span class="hljs-class"><span class="hljs-keyword">contract</span> <span class="hljs-title">UniswapExample</span> </span>{
    <span class="hljs-keyword">address</span> <span class="hljs-keyword">private</span> factory = <span class="hljs-number">0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f</span>;
    <span class="hljs-keyword">address</span> <span class="hljs-keyword">private</span> dai = <span class="hljs-number">0x6B175474E89094C44Da98b954EedeAC495271d0F</span>;
    <span class="hljs-keyword">address</span> <span class="hljs-keyword">private</span> weth = <span class="hljs-number">0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2</span>;

    <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">getTokenReserves</span>(<span class="hljs-params"></span>) <span class="hljs-title"><span class="hljs-keyword">external</span></span> <span class="hljs-title"><span class="hljs-keyword">view</span></span> <span class="hljs-title"><span class="hljs-keyword">returns</span></span> (<span class="hljs-params"><span class="hljs-keyword">uint</span>, <span class="hljs-keyword">uint</span></span>) </span>{
        <span class="hljs-keyword">address</span> pair = UniswapV2Factory(factory).getPair(dai, weth);
        (<span class="hljs-keyword">uint</span> reserve0, <span class="hljs-keyword">uint</span> reserve1, ) = UniswapV2Pair(pair).getReserves();
        <span class="hljs-keyword">return</span> (reserve0, reserve1);
    }
}
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