问题
How can I get PHP to evaluate a static variable in double quotes?
I want to do something like this:
log(\"self::$CLASS $METHOD entering\");
I\'ve tried all sorts of {} combos to get the variable value of self::$CLASS, but nothing has worked. I\'ve currently settled with string concatenation but it is a pain to type:
log(self::$CLASS . \" $METHOD entering\");
回答1:
Sorry, you can't do that. It only works for simple expressions. See here.
回答2:
Unfortunately there is no way how to do this yet. Example in one of answers here will not work, because {${self::$CLASS}} will not returns content of self::$CLASS, but will returns content of variable with name in self::$CLASS.
Here is an example, which does not returns myvar, but aaa:
$myvar = 'aaa';
self::$CLASS = 'myvar';
echo "{${self::$CLASS}}";
回答3:
I don’t know the answer to your question, but you can show the class name and method using the __METHOD__ magic constant.
回答4:
Use an anonymous identity function stored in a variable. This way you will have $ immediately after {:
$I = function($v) { return $v; };
$interpolated = "Doing {$I(self::FOO)} with {$I(self::BAR)}";
(I am using class constants in this example but this will work with static variables too).
回答5:
Just live with the concatenation. You'd be surprised how inefficient variable interpolation in strings can be.
And while this could fall under the umbrella of pre-optimization or micro-optimization, I just don't think you actually gain any elegance in this example.
Personally, if I'm gonna make a tiny optimization of one or the other, and my choices are "faster" and "easier to type" - I'm gonna choose "faster". Because you only type it a few times, but it's probably going to execute thousands of times.
回答6:
I know this is an old question but I find it odd that noone has suggested the [sprintf][1] function yet.
say:
<?php
class Foo {
public static $a = 'apple';
}
you would use it with:
echo sprintf( '$a value is %s', Foo::$a );
so on your example its:
log(
sprintf ( ' %s $METHOD entering', self::$CLASS )
);
回答7:
Yes this can be done:
log("{${self::$CLASS}} $METHOD entering");
来源：https://stackoverflow.com/questions/1267093/php-static-variables-in-double-quotes