php - ${ } 在 PHP 语法中是什么意思？

Question

我用PHP很长时间了，但我只是看到了类似的东西，

${  } 

确切地说，我是在一个 PHP Mongo 页面中看到的:

$m = new Mongo("mongodb://${username}:${password}@host");

那么，${ } 是做什么的？使用 Google 或在 PHP 文档中搜索 $、{ 和 } 等字符非常困难。

Answer 1

${ }(美元符号大括号)被称为 Simple syntax .

It provides a way to embed a variable, an array value, or an objectproperty in a string with a minimum of effort.

If a dollar sign ($) is encountered, the parser will greedily take asmany tokens as possible to form a valid variable name. Enclose thevariable name in curly braces to explicitly specify the end of thename.

<?php
$juice = "apple";

echo "He drank some $juice juice.".PHP_EOL;
// Invalid. "s" is a valid character for a variable name, but the variable is $juice.
echo "He drank some juice made of $juices.";
// Valid. Explicitly specify the end of the variable name by enclosing it in braces:
echo "He drank some juice made of ${juice}s.";
?>

The above example will output:

He drank some apple juice.
He drank some juice made of .
He drank some juice made of apples.