hi，我是温新，一名PHPer

对返回值的限制

如果一个方法不需要任何返回值，可以使用never进行限制。使用never表示该方式不能有返回值，如写了返回值，则报错。

<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important"><?</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">php</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">class</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">Person</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">    <span style="box-sizing: border-box;color: rgb(98, 151, 85) !important">// 限制不能有返回值</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">   public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">index</span>():<span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">never</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">   {</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">   }</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span>

对常量的限制

<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important"><?</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">php</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">    </span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">class</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">Person</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">    <span style="box-sizing: border-box;color: rgb(98, 151, 85) !important">// 使用final限定常量</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">    final</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">const</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">PI</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">3.14</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">class</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">Lucy</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">extends</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Person</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">    <span style="box-sizing: border-box;color: rgb(98, 151, 85) !important">// 子类继承父类并修改常量</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">   public</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">const</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">PI</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">6666</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(98, 151, 85) !important">// 报错</span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">echo</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Lucy</span>::<span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">PI</span>;</span>

对于可以修改常量的值而言，这本身就是一个BUG。在父类中，如果不使用final对常量进行限制，子类继承父类可以对常量值进行修改。

对于新鲜的东西保持着热忱，不断加以练习