英文:
What is a temporary expression in PHP?
问题
当我运行以下代码时，
<?php
const nums = [1, 2, 3];
nums[0] = 50;
它给我返回以下错误：
Fatal error: Cannot use temporary expression in write context in <file> on line 4
我的问题是，在PHP中，"temporary expression" 究竟是什么意思？我已经尝试在PHP文档中搜索答案，但没有关于这个错误的具体说明。
我只是不明白这个错误究竟是什么意思？
英文:
When I run the following code,
<?php
const nums = [1, 2, 3];
nums[0] = 50;
it gives me the following error:
Fatal error: Cannot use temporary expression in write context in <file> on line 4
My question is what exacty is a temporary expression in PHP? I've tried searching the documentation of PHP for an answer but there is nothing mentioned there regarding this error.
I just can't understand what exactly does this error mean?
答案1
得分: 2
这条消息是泄露内部信息的一部分。如果你在PHP源代码中查找这个字符串，你会找到明确的单元测试，说明在这些情境下会抛出错误：
-
枚举防止取消设置值
枚举 Foo: int { 项目 栏 = 0; } 取消设置(Foo::Bar->value); -
临时引用传递的尺寸提取是不允许的
$fn = function(&$ref) {}; $fn([0, 1][0]); -
临时引用传递的属性提取是不允许的
$fn = function(&$ref) {}; $fn([0, 1]->prop); -
不允许对临时表达式进行写入
[0, 1][0] = 1;
这条消息让人困惑，因为它不是由对常量的直接写入触发的。事实上，单独的 FOO = 2; 就是一个解析错误。
英文:
This message is a bit of a leaked internal. If you look for the string in PHP source code, you'll find explicit unit tests that illustrate the error being thrown in these contexts:
-
Enum prevent unsetting value
enum Foo: int { case Bar = 0; } unset(Foo::Bar->value); -
Passing a dimension fetch on a temporary by reference is not allowed
$fn = function(&$ref) {}; $fn([0, 1][0]); -
Passing a property fetch on a temporary by reference is not allowed
$fn = function(&$ref) {}; $fn([0, 1]->prop); -
Writing to a temporary expression is not allowed
[0, 1][0] = 1;
The message is confusing because it isn't directly triggered by writing to a constant. In fact, FOO = 2; alone is a parse error.
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