PHP8.1新特性之Readonly Properties（只读属性）
只读属性必须要有类型限制；
只读属性只能在构造函数中初始化赋值；
只读属性不能有默认值
构造函数中赋值
<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"><?php<br></br><br></br>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(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">__construct</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">// 变量的类型必须进行设置</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">// 否则会报错</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">public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">readonly</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">string</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span>,</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">readonly</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">int</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$age</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><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(224, 108, 117) !important">$person</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">new</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Person</span>(<span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'lucy'</span>, <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">18</span>);</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">echo</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$person</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">name</span>, <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$person</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">age</span>;</span>
声明再赋值
<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><?php<br></br><br></br>class Person</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">{</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> public readonly string <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> public readonly int <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$age</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> public <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">function</span> __construct(string <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span>, int <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$age</span>)</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> {</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$this</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">-</span>>name <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$this</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">-</span>>age <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$age</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"> }</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px">}</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box"></span></span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$person</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> new Person(<span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'lucy'</span>, <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">18</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(232, 191, 106) !important">echo</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$person</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">-</span>>name, <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$person</span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">-</span>>age;</span>
对只读属性设置默认值会报错
<span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important"><?php<br></br><br></br>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(198, 120, 221) !important"> public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">readonly</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">string</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'lucy'</span>;</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important"> public</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">readonly</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">int</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$age</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"> 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">__construct</span>(<span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">string</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</span>, <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">int</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$age</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(224, 108, 117) !important">$this</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">name</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$name</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(224, 108, 117) !important">$this</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">age</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$age</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 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(224, 108, 117) !important">$person</span> <span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">=</span> <span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">new</span> <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">Person</span>(<span style="box-sizing: border-box;color: rgb(152, 195, 121) !important">'lucy'</span>, <span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">18</span>);</span><br></br><span style="box-sizing: border-box;color: rgb(171, 178, 191);padding-right: 0.1px"><span style="box-sizing: border-box;color: rgb(198, 120, 221) !important">echo</span> <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$person</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">name</span>, <span style="box-sizing: border-box;color: rgb(224, 108, 117) !important">$person</span><span style="box-sizing: border-box;color: rgb(86, 182, 194) !important">-></span><span style="box-sizing: border-box;color: rgb(209, 154, 102) !important">age</span>;</span>
报错信息：Fatal error: Readonly property Person::$name cannot have default value in
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