Also not necessarily a function, both rust and js support closures in brackets.

This correspondence is made abundantly clear by C++ which explicitly defines its lambda functions ”as if” they desugared into objects of appropriate anonymous compiler-generated struct/class types. Also Java, which has had closures since day one, but used to call them ”anonymous inner classes” and forced people to use a ridiculously verbose syntax to define them.

This is literally how Delphi implements closures/anonymous methods.

The compiler will generate a class with fields for whatever variables are captured, and then instantiate it for you, assign the fields etc.

If you define your function reference as a type (as it's called), you can even inherit[1] from it and add additional overloads to the inherited class, to make it do multiple things.

[1]: https://delphisorcery.blogspot.com/2015/06/anonymous-method-...