串联运算符 [英] Concatenation Operator

问题描述

这可能是一个愚蠢的问题，但它令我震惊，在这里我问。

This might be a silly question but it struck me, and here i ask.

<?php
  $x="Hi";
  $y=" There";
  $z = $x.$y;
  $a = "$x$y";
  echo "$z"."<br />"."$a";
?>

$ z 使用提供的传统串联运算符通过php和连接起来，相反$ a不会，

$z uses the traditional concatenation operator provided by php and concatenates, conversely $a doesn't,

我的问题：

1. 通过不使用串联运算符会影响性能吗？

1. by not using the concatenation operator, does it effect the performance?

如果不是这样，为什么根本没有串联运算符。

If it doesn't why at all have the concatenation operator.

为什么一种工作方式有两种实现方式？

Why have 2 modes of implementation when one does the work?

推荐答案

1. 仅需一点点，因为PHP必须解析整个字符串以查找变量，而使用串联时，它只是将两个变量在一起。因此，它对性能的影响很小，但是对于大多数事情而言却并不明显。

1. Only slightly, since PHP has to parse the entire string looking for variables, while with concatenation, it just slaps the two variables together. So there's a tiny performance hit, but it's not noticeable for most things.

连接诸如 $ _ SERVER之类的变量要容易得多。 ''DOCUMENT_ROOT'] 使用串联运算符（带引号，您必须将变量括在方括号中或删除数组索引中的单引号；加上它只会使字符串看起来很难看）。此外，串联运算符还为格式化提供了更大的灵活性。例如，您可以将长字符串文字分解为多行，然后将其不同部分连接起来：

It's a lot easier to concatenate variables like $_SERVER['DOCUMENT_ROOT'] using the concatenation operator (with quotes, you have to surround the variable in brackets or remove the single quotes in the array index; plus it just makes the string look all ugly). Plus, the concatenation operator allows more flexibility for formatting. For example, you can break up a long string literal onto multiple lines and then concatenate the different parts of it:

$blah = "This is a really really long string. I don't even know how " .
    "long it is, but it's really long. Like, longer than an eel " .
    "or even a boa constrictor. Wow.";

您还可以使用串联运算符直接在字符串文字中包含函数的返回值（您可以

You can also use the concatenation operator to directly include return values from functions in a string literal (you can't include a function call in a double-quoted string), like this:

$blah = "This has a " . fn_call() . " result, which can't go in the quotes.";

我不确定我是否完全理解您在这里的要求，但是我可以说PHP是从Perl借来的很多东西，而Perl的口头禅是有多种方法可以做到这一点。

I'm not sure I entirely understand what you're asking here, but I can say that PHP borrows a lot of things from Perl, and one of Perl's mantras is "There's more than one way to do it."

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