What is the difference between these PHP string interpolation syntaxes

Question

What is the difference between "${varname}" and "{$varname}" in PHP's string interpolation? (notice the position of the $)

The php docs say that you can use either, but doesn't clearly explain what the difference between these two methods is. Is there actually a difference?

Answer 1

The first one is interpolation plus variable variable (dynamic variable), meaning you can use expressions here to define the name of the variable you want to interpolate "${func()}" While the second one syntax is used to distinct variable from the text "some{$variable}text". You can actually combine them:

function func(){
    return 'foo';
}
$foo = 'bar';
echo "some{${func()}}text";

Outputs: somebartext