CODEWITHSUNDEEP
typesf#overloading
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sdgfsdh

Reputation: 37045

In F#, can two functions with different arity and return types share a name?

In F#, can two functions with different arity and return types share a name?

For example, with 2 arguments, f returns an int: 

let f (x:int) (y:int) : int = x + y

But with 3 arguments, f returns a bool: 

let f (x:bool) (y:bool) (z:bool) : bool = x & y & z

It seems like the return type should be inferable by the number of arguments given, but I get the compilation error:

Duplicate definition of value 'f'

Is this a limitation of F#?

Upvotes: 3

Views: 1040

Answers (1)

Gus
Gus

Reputation: 26174

Let's analyse both features:

  • Different return type:

This is not trivial in F# as in other functional languages, but it's possible and at some point they make sense. Typical examples are the math operators, they return different types based on the input parameter types, so in the end what you have is a single generic function. This in not the same idea as method overloading where you have many methods which share the name.

  • Different number of arguments:

This is even less trivial, also in other functional languages with automatic currying, because it will conflict with that feature. Still there are some (few) cases where they might make sense, here's an example coming from Haskell.

  • Both at the same time:

This makes practically no sense, the idea behind overloaded functions is to have a relationship between the types of the input (and maybe also the output) arguments of the different overloads which would feel as a single generic function. So in this case it resemble more .NET method overloading which by the way is a feature supported in F#.

Finally, using some hacks you can encode your example in F#:

let f (x:int) (y:int) : int = x + y
let g (x:bool) (y:bool) (z:bool) : bool = x & y & z

type T = T with
    static member ($) (T, x) = fun y   -> f x y
    static member ($) (T, x) = fun y z -> g x y z

let inline myFunc x y = (T $ x) y

let result1 = myFunc 3 5
let result2 = myFunc true false true

But again, I don't think it's a good idea.

Upvotes: 5

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