PHP 数组索引：$array[$index] vs $array["$index"] vs $array["{$index}"]
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PHP array indexing: $array[$index] vs $array["$index"] vs $array["{$index}"]
提问by svec
What is the difference, if any, between these methods of indexing into a PHP array:
这些索引到 PHP 数组的方法之间有什么区别（如果有）：
$array[$index]
$array["$index"]
$array["{$index}"]
I'm interested in both the performance and functional differences.
我对性能和功能差异都很感兴趣。
Update:
更新：
(In response to @Jeremy) I'm not sure that's right. I ran this code:
（回应@Jeremy）我不确定这是对的。我运行了这个代码：
$array = array(100, 200, 300);
print_r($array);
$idx = 0;
$array[$idx] = 123;
print_r($array);
$array["$idx"] = 456;
print_r($array);
$array["{$idx}"] = 789;
print_r($array);
And got this output:
并得到这个输出：
Array
(
[0] => 100
[1] => 200
[2] => 300
)
Array
(
[0] => 123
[1] => 200
[2] => 300
)
Array
(
[0] => 456
[1] => 200
[2] => 300
)
Array
(
[0] => 789
[1] => 200
[2] => 300
)
回答by
see @svec and @jeremy above. All array indices are of type 'int' first, then type 'string', and will be cast to that as PHP sees fit.
请参阅上面的@svec 和@jeremy。所有数组索引都首先是“int”类型，然后是“string”类型，并会在 PHP 认为合适的情况下转换为该类型。
Performance wise, $index should be faster than "$index" and "{$index}" (which are the same).
性能方面， $index 应该比 "$index" 和 "{$index}" （它们是相同的）更快。
Once you start a double-quote string, PHP will go into interpolation mode and treat it as a string first, but looking for variable markers ($, {}, etc) to replace from the local scope. This is why in most discussions, true 'static' strings should always be single quotes unless you need the escape-shortcuts like "\n" or "\t", because PHP will not need to try to interpolate the string at runtime and the full string can be compiled statically.
一旦您开始一个双引号字符串，PHP 将进入插值模式并首先将其视为字符串，但会在本地范围内寻找变量标记（$、{} 等）以进行替换。这就是为什么在大多数讨论中，真正的“静态”字符串应该始终是单引号，除非您需要像 "\n" 或 "\t" 这样的转义快捷方式，因为 PHP 不需要在运行时尝试插入字符串，并且完整的字符串可以静态编译。
In this case, doublequoting will first copy the $index into that string, then return the string, where directly using $index will just return the string.
在这种情况下，双引号将首先将 $index 复制到该字符串中，然后返回该字符串，而直接使用 $index 只会返回该字符串。
回答by svec
I timed the 3 ways of using an index like this:
我对使用索引的 3 种方式进行计时：
for ($ii = 0; $ii < 1000000; $ii++) {
// TEST 1
$array[$idx] = $ii;
// TEST 2
$array["$idx"] = $ii;
// TEST 3
$array["{$idx}"] = $ii;
}
The first set of tests used $idx=0, the second set used $idx="0", and the third set used $idx="blah". Timing was done using microtime()diffs. I'm using WinXP, PHP 5.2, Apache 2.2, and Vim. :-)
使用第一组测试，使用$idx=0第二组，使用$idx="0"第三组$idx="blah"。时间是使用microtime()差异完成的。我使用的是 WinXP、PHP 5.2、Apache 2.2 和 Vim。:-)
And here are the results:
结果如下：
Using $idx = 0
使用 $idx = 0
$array[$idx] // time: 0.45435905456543 seconds
$array["$idx"] // time: 1.0537171363831 seconds
$array["{$idx}"] // time: 1.0621709823608 seconds
ratio "$idx" / $idx // 2.3191287282497
ratio "{$idx}" / $idx // 2.3377348193858
Using $idx = "0"
使用 $idx = "0"
$array[$idx] // time: 0.5107250213623 seconds
$array["$idx"] // time: 0.77445602416992 seconds
$array["{$idx}"] // time: 0.77329802513123 seconds
ratio "$idx" / $idx // = 1.5163855142717
ratio "{$idx}" / $idx // = 1.5141181512285
Using $idx = "blah"
使用 $idx = "blah"
$array[$idx] // time: 0.48077392578125 seconds
$array["$idx"] // time: 0.73676419258118 seconds
$array["{$idx}"] // time: 0.71499705314636 seconds
ratio "$idx" / $idx // = 1.5324545551923
ratio "{$idx}" / $idx // = 1.4871793473086
So $array[$idx]is the hands-down winner of the performance competition, at least on my machine. (The results were very repeatable, BTW, I ran it 3 or 4 times and got the same results.)
所以$array[$idx]是性能竞争的双手向下赢家，至少在我的机器上。（结果非常可重复，顺便说一句，我运行了 3 到 4 次并得到了相同的结果。）
回答by Akira
I believe from a performance perspective that $array["$index"] is faster than $array[$index] See Best practices to optimize PHP code performance
我相信从性能的角度来看， $array["$index"] 比 $array[$index] 更快，请参阅优化 PHP 代码性能的最佳实践
Don't believe everything you read so blindly... I think you misinterpreted that. The article says $array['index'] is faster than $array[index] where index is a string, not a variable. That's because if you don't wrap it in quotes PHP looks for a constant var and can't find one so assumes you meant to make it a string.
不要盲目相信您阅读的所有内容...我认为您误解了这一点。文章说 $array['index'] 比 $array[index] 快，其中 index 是一个string，而不是一个变量。那是因为如果你不把它用引号括起来，PHP 会寻找一个常量 var 并且找不到一个，所以假设你打算把它变成一个字符串。
回答by Jeremy Ruten
When will the different indexing methods resolve to different indices?
不同的索引方法何时会解析为不同的索引？
According to http://php.net/types.array, an array index can only be an integer or a string. If you try to use a float as an index, it will truncate it to integer. So if $indexis a float with the value 3.14, then $array[$index]will evaluate to $array[3]and $array["$index"]will evaluate to $array['3.14']. Here is some code that confirms this:
根据http://php.net/types.array，数组索引只能是整数或字符串。如果您尝试使用浮点数作为索引，它会将其截断为整数。所以，如果$index是价值3.14浮动，然后$array[$index]将评估对$array[3]和$array["$index"]将评估到$array['3.14']。这是一些确认这一点的代码：
$array = array(3.14 => 'float', '3.14' => 'string');
print_r($array);
$index = 3.14;
echo $array[$index]."\n";
echo $array["$index"]."\n";
The output:
输出：
Array([3] => float [3.14] => string)
float
string
回答by Jeremy Ruten
Response to the Update:
对更新的回应：
Oh, you're right, I guess PHP must convert array index strings to numbers if they contain only digits. I tried this code:
哦，你说得对，我猜如果数组索引字符串只包含数字，PHP 必须将它们转换为数字。我试过这个代码：
$array = array('1' => 100, '2' => 200, 1 => 300, 2 => 400);
print_r($array);
And the output was:
输出是：
Array([1] => 300 [2] => 400)
I've done some more tests and found that if an array index (or key) is made up of only digits, it's always converted to an integer, otherwise it's a string.
我做了一些更多的测试，发现如果数组索引（或键）只由数字组成，它总是被转换为整数，否则它是一个字符串。
ejunker:
电子垃圾：
Can you explain why that's faster? Doesn't it take the interpreter an extra step to parse "$index" into the string to use as an index instead of just using $index as the index?
你能解释一下为什么更快吗？解释器是否需要额外的步骤将“$index”解析为字符串以用作索引而不是仅使用 $index 作为索引？
回答by Jeremy Ruten
If $index is a string there is no difference because $index, "$index", and "{$index}" all evaluate to the same string. If $index is a number, for example 10, the first line will evaluate to $array[10] and the other two lines will evaluate to $array["10"] which is a different element than $array[10].
如果 $index 是字符串，则没有区别，因为 $index、"$index" 和 "{$index}" 都计算为相同的字符串。如果 $index 是一个数字，例如 10，第一行的计算结果为 $array[10]，其他两行的计算结果为 $array["10"]，这是与 $array[10] 不同的元素。
回答by ejunker
I believe from a performance perspective that $array["$index"] is faster than $array[$index] See Best practices to optimize PHP code performance
我相信从性能的角度来看， $array["$index"] 比 $array[$index] 更快，请参阅优化 PHP 代码性能的最佳实践
Another variation that I use sometimes when I have an array inside a string is:
当我在字符串中有数组时，我有时使用的另一个变体是：
$str = "this is my string {$array["$index"]}";
Edit: What I meant to say is $row['id'] is faster than $row[id]
编辑：我的意思是 $row['id'] 比 $row[id] 快
