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<meta property="og:description" content="函数柯里化定义函数柯里化（function currying）又称部分求值。一个currying的函数首先会接受一些参数，接受了这些参数后， 该函数并不会立即求值，而是继续返回另外一个函数，刚才传入的参数在函数形成的闭包里被保存起来。待到函数真正需要求值的时候，之前传入的参数都会被一次性用于求值。 把接受多个参数的函数变换成接受一个单一参数（最初函数的第一个参数）的函数，并且返回接受余下的参数而且">
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<h3 id="函数柯里化定义"><a href="#函数柯里化定义" class="headerlink" title="函数柯里化定义"></a>函数柯里化定义</h3><p>函数柯里化（function currying）又称部分求值。一个currying的函数首先会接受一些参数，接受了这些参数后，</p>
<p>该函数并不会立即求值，而是继续返回另外一个函数，刚才传入的参数在函数形成的闭包里被保存起来。待到函数真正需要求值的时候，之前传入的参数都会被一次性用于求值。</p>
<p>把接受多个参数的函数变换成接受一个单一参数（最初函数的第一个参数）的函数，并且返回接受余下的参数而且返回结果的新函数。</p>
<p>顾名思义，柯里化其实本身是固定一个可以预期的参数，并返回一个特定的函数，处理批特定的需求。这增加了函数的适用性，但同时也降低了函数的适用范围。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">add</span>(<span class="params">x,y</span>)</span>{</span><br><span class="line"> <span class="keyword">return</span> x + y;</span><br><span class="line">}</span><br><span class="line"><span class="comment">// 函数只传入一个参数的时候实现加法</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">curry</span>(<span class="params">x</span>)</span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="function"><span class="keyword">function</span>(<span class="params">y</span>)</span>{</span><br><span class="line"> <span class="keyword">return</span> x + y;</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"><span class="keyword">var</span> add2 = curry(<span class="number">1</span>);</span><br><span class="line">add2(<span class="number">1</span>) <span class="comment">// 2 即curry(1)(1)</span></span><br></pre></td></tr></table></figure>
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<h3 id="函数柯里化实践"><a href="#函数柯里化实践" class="headerlink" title="函数柯里化实践"></a>函数柯里化实践</h3><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 通过以上简单介绍我们大概了解了，函数柯里化基本是在做这么一件事情：只传递给函数一部分参数来调用它，让它返回一个函数去处理剩下的参数。用公式表示就是我们要做的事情其实是</span></span><br><span class="line"></span><br><span class="line">fn(a,b,c,d)=>fn(a)(b)(c)(d)；</span><br><span class="line"></span><br><span class="line">fn(a,b,c,d)=>fn(a，b)(c)(d)；</span><br><span class="line"></span><br><span class="line">fn(a,b,c,d)=>fn(a)(b，c，d)；</span><br><span class="line"></span><br><span class="line">......</span><br><span class="line"></span><br><span class="line"><span class="comment">// 再或者这样：</span></span><br><span class="line"></span><br><span class="line">fn(a,b,c,d)=>fn(a)(b)(c)(d)()；</span><br><span class="line"></span><br><span class="line">fn(a,b,c,d)=>fn(a)；fn(b)；fn(c)；fn(d)；fn()；</span><br></pre></td></tr></table></figure>
<blockquote>
<p>通用的函数柯里化版本</p>
</blockquote>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 这里需要传入长度</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">curry</span>(<span class="params">fn, length, ary</span>) </span>{</span><br><span class="line"> length = length || fn.length;</span><br><span class="line"> ary = ary || [];<span class="comment">//记录所有传入的参数</span></span><br><span class="line"> <span class="keyword">var</span> slice = <span class="built_in">Array</span>.prototype.slice;</span><br><span class="line"> <span class="keyword">return</span> <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">arguments</span>.length < length) {</span><br><span class="line"> <span class="built_in">Array</span>.prototype.push.apply(ary, slice.call(<span class="built_in">arguments</span>));<span class="comment">//每次把参数合并到ary数组中</span></span><br><span class="line"> <span class="keyword">return</span> curry(fn, length - <span class="built_in">arguments</span>.length, ary)<span class="comment">//把还需传参的长度和已有参数数组传入curry，递归调用</span></span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">return</span> fn.apply(<span class="keyword">this</span>, ary.concat(slice.call(<span class="built_in">arguments</span>))); <span class="comment">//调用求职函数，记得把此次传入的参数合并到ary数组再计算</span></span><br><span class="line"> }</span><br><span class="line"> };</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> total = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">let</span> total = <span class="number">0</span>;</span><br><span class="line"> [].slice.call(<span class="built_in">arguments</span>).forEach(<span class="function"><span class="params">item</span> =></span> {</span><br><span class="line"> total += item;</span><br><span class="line"> });</span><br><span class="line"> <span class="keyword">return</span> total;</span><br><span class="line"> };</span><br><span class="line"> <span class="keyword">let</span> fn = curry(total, <span class="number">4</span>);</span><br><span class="line"> fn(<span class="number">1</span>)(<span class="number">2</span>)(<span class="number">3</span>)(<span class="number">4</span>);<span class="comment">//10</span></span><br><span class="line"> fn(<span class="number">1</span>,<span class="number">2</span>)(<span class="number">3</span>)(<span class="number">4</span>);<span class="comment">//10</span></span><br></pre></td></tr></table></figure>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 这里是无参数时开始计算所有的cost</span></span><br><span class="line"><span class="keyword">var</span> currying = <span class="function"><span class="keyword">function</span>(<span class="params">fn</span>)</span>{</span><br><span class="line"> <span class="keyword">var</span> args = [];</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">return</span> <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="keyword">if</span>(<span class="built_in">arguments</span>.length === <span class="number">0</span>){</span><br><span class="line"> <span class="keyword">return</span> fn.apply(<span class="keyword">this</span>, args);</span><br><span class="line"> }<span class="keyword">else</span>{</span><br><span class="line"> [].push.apply(args, <span class="built_in">arguments</span>);</span><br><span class="line"> <span class="keyword">return</span> <span class="built_in">arguments</span>.callee;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">};</span><br><span class="line"><span class="keyword">var</span> cost = (<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="keyword">var</span> money = <span class="number">0</span>;</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">return</span> <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="keyword">for</span>(<span class="keyword">var</span> i = <span class="number">0</span>, l = <span class="built_in">arguments</span>.length; i < l; i++){</span><br><span class="line"> money += <span class="built_in">arguments</span>[i];</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> money;</span><br><span class="line"> }</span><br><span class="line">}());</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> cost = currying(cost);<span class="comment">//转化为currying函数</span></span><br><span class="line"></span><br><span class="line">cost(<span class="number">100</span>);<span class="comment">//未真正求值</span></span><br><span class="line">cost(<span class="number">200</span>);<span class="comment">//未真正求值</span></span><br><span class="line">cost(<span class="number">300</span>);<span class="comment">//未真正求值</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(cost());<span class="comment">//求值并输出：600</span></span><br></pre></td></tr></table></figure>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 和toString().valueOf()时计算和是一样的道理</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">add</span>(<span class="params">num</span>)</span>{</span><br><span class="line"> <span class="keyword">var</span> _add = <span class="function"><span class="keyword">function</span>(<span class="params">args</span>)</span>{</span><br><span class="line"> num+=args;</span><br><span class="line"> <span class="keyword">return</span> <span class="built_in">arguments</span>.callee;</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// (function foo(args){num+=args return foo;})</span></span><br><span class="line"> <span class="keyword">var</span> _add =(<span class="function"><span class="keyword">function</span> <span class="title">foo</span>(<span class="params">args</span>)</span>{num+=args; <span class="keyword">return</span> foo;})</span><br><span class="line"> _add.toString = _add.valueOf = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="keyword">return</span> num;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span> _add;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="为了减少函数传参，同时将一些固定参数私有化"><a href="#为了减少函数传参，同时将一些固定参数私有化" class="headerlink" title="为了减少函数传参，同时将一些固定参数私有化"></a>为了减少函数传参，同时将一些固定参数私有化</h3><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">curry</span>(<span class="params">fn, args</span>) </span>{</span><br><span class="line"> <span class="comment">// 获取函数需要的参数长度</span></span><br><span class="line"> <span class="keyword">let</span> length = fn.length;</span><br><span class="line"></span><br><span class="line"> args = args || [];</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> <span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">let</span> subArgs = args.slice(<span class="number">0</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 拼接得到现有的所有参数</span></span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i < <span class="built_in">arguments</span>.length; i++) {</span><br><span class="line"> subArgs.push(<span class="built_in">arguments</span>[i]);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 判断参数的长度是否已经满足函数所需参数的长度</span></span><br><span class="line"> <span class="keyword">if</span> (subArgs.length >= length) {</span><br><span class="line"> <span class="comment">// 如果满足，执行函数</span></span><br><span class="line"> <span class="keyword">return</span> fn.apply(<span class="keyword">this</span>, subArgs);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// 如果不满足，递归返回科里化的函数，等待参数的传入</span></span><br><span class="line"> <span class="keyword">return</span> curry.call(<span class="keyword">this</span>, fn, subArgs);</span><br><span class="line"> }</span><br><span class="line"> };</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// es6实现</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">curry</span>(<span class="params">fn, ...args</span>) </span>{</span><br><span class="line"> <span class="keyword">return</span> fn.length <= args.length ? fn(...args) : curry.bind(<span class="literal">null</span>, fn, ...args);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="函数柯里化的优点"><a href="#函数柯里化的优点" class="headerlink" title="函数柯里化的优点"></a>函数柯里化的优点</h3><ol>
<li><p>延迟计算
可以传递需要的参数，等到何时想要结果，再一并计算。</p>
</li>
<li><p>参数复用
有些参数相同，只需要传递一遍即可，不需要每次都传，太繁琐。</p>
</li>
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<p><span>本文标题:</span><a href="/js%E5%87%BD%E6%95%B0%E6%9F%AF%E9%87%8C%E5%8C%96.html">js函数柯里化</a></p>
<p><span>文章作者:</span><a href="/" title="访问 陈宇（cosyer） 的个人博客">陈宇（cosyer）</a></p>
<p><span>发布时间:</span>2018年11月22日 - 09:11</p>
<p><span>最后更新:</span>2020年07月05日 - 00:07</p>
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