php - “{$var1}someString”和“$var1someString”有什么区别？

Question

我可以区分

echo "{$var1}someString" // here the variable is $var1
echo "$var1someString"   // here the variable is $var1someString

问题是为什么要使用{}？它仅适用于{}. 它不适用于(). 有什么特别之处{ }？

Answer 1

花括号{}以这种方式用于标识字符串中的变量：

echo "{$var1}someString"

如果你看：

echo "$var1someString"

PHP 不可能确定您想要 echo $var1，它会将所有这些都作为变量名。

您可以改为连接变量：

echo $var1 . "someString"

它不能()仅仅因为 PHP 设计者选择{}.

Answer 2

根据string的文档，卷曲部分称为复杂语法。它基本上允许您在字符串中使用复杂的表达式。

文档中的示例：

<?php
// Show all errors
error_reporting(E_ALL);

$great = 'fantastic';

// Won't work, outputs: This is { fantastic}
echo "This is { $great}";

// Works, outputs: This is fantastic
echo "This is {$great}";
echo "This is ${great}";

// Works
echo "This square is {$square->width}00 centimeters broad."; 


// Works, quoted keys only work using the curly brace syntax
echo "This works: {$arr['key']}";


// Works
echo "This works: {$arr[4][3]}";

// This is wrong for the same reason as $foo[bar] is wrong  outside a string.
// In other words, it will still work, but only because PHP first looks for a
// constant named foo; an error of level E_NOTICE (undefined constant) will be
// thrown.
echo "This is wrong: {$arr[foo][3]}"; 

// Works. When using multi-dimensional arrays, always use braces around arrays
// when inside of strings
echo "This works: {$arr['foo'][3]}";

// Works.
echo "This works: " . $arr['foo'][3];

echo "This works too: {$obj->values[3]->name}";

echo "This is the value of the var named $name: {${$name}}";

echo "This is the value of the var named by the return value of getName(): {${getName()}}";

echo "This is the value of the var named by the return value of \$object->getName(): {${$object->getName()}}";

// Won't work, outputs: This is the return value of getName(): {getName()}
echo "This is the return value of getName(): {getName()}";
?>

Answer 3

你自己解释了。这就是 php 使用的语法——仅此而已。引用文档：

复杂（卷曲）语法
只需将表达式编写成与它出现在字符串外部相同的方式，然后将其包装在 { 和 }中。由于 { 无法转义，因此只有在 $ 紧跟 { 时才能识别此语法。使用 {\$ 获取文字 {$

Answer 4

在这里{}定义这些变量不是一个简单的字符串，所以 php 获取该变量值而不是假设它是一个简单的字符串。