php PHP中关联数组的插值（双引号字符串）
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Interpolation (double quoted string) of Associative Arrays in PHP
提问by rubber boots
When interpolating PHP's string-indexed array elements (5.3.3, Win32) the following behavior may be expected or not:
插入 PHP 的字符串索引数组元素（5.3.3，Win32）时，可能会出现以下行为，也可能不会：
$ha = array('key1' => 'Hello to me');
print $ha['key1']; # correct (usual way)
print $ha[key1]; # Warning, works (use of undefined constant)
print "He said {$ha['key1']}"; # correct (usual way)
print "He said {$ha[key1]}"; # Warning, works (use of undefined constant)
print "He said $ha['key1']"; # Error, unexpected T_ENCAPSED_AND_WHITESPACE
print "He said $ha[ key1 ]"; # Error, unexpected T_ENCAPSED_AND_WHITESPACE
print "He said $ha[key1]"; # !! correct (How Comes?)
Inerestingly, the last line seems to be correct PHP code. Any explanations? Can this feature be trusted?
有趣的是，最后一行似乎是正确的 PHP 代码。有什么解释吗？这个功能可以信任吗？
编辑：现在发帖的重点是 bold face大胆面对，以减少误解。
回答by NikiC
Yes, you may trust it. All ways of interpolation a variable are covered in the documentationpretty well.
是的，你可以相信它。文档中很好地涵盖了对变量进行插值的所有方法。
If you want to have a reason why this was done so, well, I can't help you there. But as always: PHP is old and has evolved a lot, thus introducing inconsistent syntax.
如果你想知道这样做的原因，好吧，我不能帮你。但与往常一样：PHP 很旧并且已经发展了很多，因此引入了不一致的语法。
回答by mfonda
Yes, this is well defined behavior, and will always look for the string key 'key', and not the value of the (potentially undefined) constant key.
是的，这是定义明确的行为，并且将始终查找字符串 key 'key'，而不是（可能未定义的）常量的值key。
For example, consider the following code:
例如，考虑以下代码：
$arr = array('key' => 'val');
define('key', 'defined constant');
echo "$arr[key] within string is: $arr[key]";
This will output the following:
这将输出以下内容：
$arr[key] within string is: val
That said, it's probably not best practice to write code like this, and instead either use:
也就是说，编写这样的代码可能不是最佳实践，而是使用：
$string = "foo {$arr['key']}"
or
或者
$string = 'foo ' . $arr['key']
syntax.
句法。
回答by mario
The last one is a special case handled by the PHP tokenizer. It does not look up if any constant by that name was defined, it always assumes a string literal for compatibility with PHP3 and PHP4.
最后一个是由 PHP 标记器处理的特殊情况。它不会查找是否定义了该名称的任何常量，它始终假定字符串文字以与 PHP3 和 PHP4 兼容。
回答by aqm
To answer your question, yes, yes it can, and much like implode and explode, php is very very forgiving... so inconsistency abound
回答你的问题，是的，是的，它可以，就像内爆和爆炸一样，php非常宽容......所以不一致比比皆是
And I have to say I like PHP's interpolation for basical daisy punching variables into strings then and there,
我不得不说我喜欢 PHP 的插值，用于将基本雏菊变量插入字符串，然后和那里，
However if your doing only string variable interpolation using a single array's objects, it may be easier to write a template which you can daisy print a specific object variables into (like in say javascript or python) and hence explicit control over the variable scope and object being applied to the string
但是，如果您只使用单个数组的对象进行字符串变量插值，则编写一个模板可能会更容易，您可以将特定对象变量打印到其中（例如在 javascript 或 python 中），从而显式控制变量范围和对象应用于字符串
I though this guy's isprintf really useful for this kind of thing
我虽然这家伙的 isprintf 对这种事情真的很有用
http://www.frenck.nl/2013/06/string-interpolation-in-php.html
http://www.frenck.nl/2013/06/string-interpolation-in-php.html
<?php
$values = array(
'who' => 'me honey and me',
'where' => 'Underneath the mango tree',
'what' => 'moon',
);
echo isprintf('%(where)s, %(who)s can watch for the %(what)s', $values);
// Outputs: Underneath the mango tree, me honey and me can watch for the moon
