“操作员"指的是“操作员".优先?为什么new Object()-> method()在PHP中给出语法错误? [英] "Operator" precedence? Why new Object()->method() gives a syntax error in PHP?

问题描述

让我们考虑以下代码:

<?php

class X{
    public function test(){
        return 'test';
    }
}

//This obviously works:
$x = (new X())->test();
//This does not, syntax error
$x = new X()->test();
echo $x;

为什么?

顺便说一句: 我知道它是在php 5.4中引入的

BTW: I know it was introduced in php 5.4

这与如何"无关，而与"为什么"有关-我知道第一种语法是手册中记录的语法.实际上，更多的是关于在哪里以及如何找到答案.

It's not about "how", it's about "why" - I know the first syntax is the one documented in the manual. Actually, it's more about where and how to find the answer.

根据我到目前为止所学的知识，同时在其他地方提问:

From what I've learned so far, while asking my questions elsewhere:

->实际上不是一个运算符"，它是一个令牌"或词汇令牌"-对我没有多大帮助.

The -> is not actually an "operator", it's a "token" or "lexical token" - which doesn't help me much.

第一个版本等于说:"new(DateTime()-> format())"，这显然是不好的.这表明它是关于运算符优先级"的，但是#1-->不是运算符(对吗?)，以及#2-为什么没有在任何地方对此进行记录?

The first version is equal to saying: "new (DateTime()->format())" which obviously is bad. This suggest it's about "operator precedence", but #1 - the -> is not an operator (right?), and #2 - why isn't this documented anywhere?

BTW，在 http://php.net/manual/zh/language.operators.precedence.php 中，我们可以看到新"运算符的关联性既不左也不右，都不是，我们还可以阅读不能在同等优先级的非关联运算符旁边使用"彼此之间，例如1< 2> 1在PHP中是非法的"，因此...如果->是 operator (并且是非关联的)，那么一切都会很清楚，但是是吗?操作员?如果是，那么为什么它不在上面的列表中列出( http: //php.net/manual/en/language.operators.precedence.php )?

BTW, on http://php.net/manual/en/language.operators.precedence.php we can read that the "new" operator associativity is neither left nor right, it's none, and we can also read "Operators of equal precedence that are non-associative cannot be used next to each other, for example 1 < 2 > 1 is illegal in PHP" so... if -> was an operator (and it was non-associative) then everything would be clear, but is it an operator? If it is, then why isn't it listed on the above list ( http://php.net/manual/en/language.operators.precedence.php )?

推荐答案

由于模棱两可，因此可以用两种不同的方式进行解释:

Because it's ambiguous, i.e. it can be interpreted in 2 different ways:

• 在新的X实例(您想要的实例)上调用test():

• Call test() on a new X instance (the one that you want):

$object = new X();
$x      = $object->test();

在 function X():

$object = X();
$class  = $object->test();
$x      = new $class();

奇怪的是，实际上没有办法为第二种情况编写单行代码……以下内容将不起作用:

Strangely enough, there's actually no way to write a one-liner for the second case ... the following won't work:

new (X()->test());   // syntax error
new (X()->test())(); // syntax error

但是，您仍然知道.

这篇关于“操作员"指的是“操作员".优先?为什么new Object()-> method()在PHP中给出语法错误?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！