PHP curly brace syntax for calling methods using string

Question

I saw in this SO answer that one can use a string inside curly braces to call a PHP class method so that

$player->SayHi();

Can be alternative written as:

$player->{'SayHi'}();

My questions are:

What is this syntax called in PHP? and what happens if a wrong string that does not correspond to a method is used?

Also, can I use this syntax to call non class methods?

I looked at the answers in the linked post, and there is only links to PHP callback syntax, which does not seem to cover the curly brace syntax.

Thanks,

Answer 1

It's part of variable functions. When using variable variables or variable functions, you can replace the variable with any expression that returns a string by wrapping on braces. So you can do:

$var = 'SayHi';
$player->$var();

or you can do it in one step with:

$player->{'SayHi'}();

The syntax with braces is shown in the documentation of variable variables. The example there is for a variable class property, but the same syntax is used for class methods.