It's almost impossible for me to search for an answer to this as I don't know what this syntax is called.
I have a server running a relatively old version of PHP (5.5.38) and I'm getting parse errors when I run a file that has the following:
public function foo(): array
{
...specifically the : array
suffix.
Can anyone tell me what this syntax is called (so I can research further) and which PHP version introduced it?