C# did this for extension methods and it Just Works. You just add the "this" keyword to a function in a pure-static class and you get method-like calling on the first param of that function.

If the function has to be modified in any way in order to grant permission to be used that way, then it is not quite "did this".

Equivalent means that there is no difference at the AST level between o.f(a) and f(o, a), like there is no difference in C among (a + i), a[i], i[a] and (i + a).

However, a this keyword is way better than making the programmers fraction off a parameter and move it to the other side of the function name.

A search term here is "Uniform Function Call Syntax", as present in (e.g.) D:

https://en.wikipedia.org/wiki/Uniform_Function_Call_Syntax

I completely agree with that.