CODEWITHSUNDEEP
f#
Stalin Pimentel
Stalin Pimentel

Reputation: 9

F# Scala apply method

I've seen there is a method one could use in a Scala type called apply. This would enable to call on a instance of the type as if it were a function or alike. Like for example the Scala list, one could write myList(0) for the first element in the list.

Is there anything like this in F#?

Upvotes: 1

Views: 166

Answers (1)

Ganesh Sittampalam
Ganesh Sittampalam

Reputation: 29100

F# function application is based around the FSharpFunc type internally. For example, (int -> int) is represented as FSharpFunc<int, int>.

However the F# compiler seems to somehow know the difference between a real F# function and a manual attempt to implement one, at least when the implementation language is F#.

However, I was able to fake an F# function by defining it in C#:

public class Foo : FSharpFunc<int, int>
{
    public override int Invoke(int n)
    {
        return n + 1;
    }

}

and then from F#:

> let x = Foo() :> int -> int
val x : (int -> int)

> x 3;;
val it : int = 4

I couldn't work the same trick when defining Foo in F#, even when I define it in a separate compilation unit.

The F# compiler seems to insert an attribute CompilationMapping(SourceConstructFlags.ObjectType) onto its own objects and I can't find a way to turn it off, but my C# works even if I put that attribute on manually.

Upvotes: 4

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