PHP闭包和回调

Question

I'm learning closures but I'm stuck with this:

function addPrefix($string) {
    return function($prefix) use ($string) {
        echo $prefix.$string;
    };
}
$randomstring = "a test";
$c = addPrefix($randomstring);
echo $c("This is ");

Why is $prefix concatenated? It's not even called as an argument, I just don't get it.

Answer 1

Pay attention in your example there is 2 functions. addPrefix, and an anonymous function it addPrefix returns.

So, $c is this anonymous function (returned by addPrefix), which has the $prefix argument.