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Tupled Arguments
f#compiler

Hi there!

I have a method taking an int*int-Tuple as parameter.
I have another method that has this as return type.
This works out well as long as I don't expand the parameter what the compiler doesn't take to well.

Here's the relevant code:

The call: this.CreateWall (this.GetFieldHit args.Location))

with the method GetFieldHit being: 

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member this.GetFieldHit (point:Point) = (point.X / (this.gridSize+1), point.Y / (this.gridSize+1))

succeeds only if the method CreateWall is written:

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member this.CreateWall point = 
   (new Rectangle (fst point, snd point, this.gridSize, this.gridSize), this.mouseDirection)


but fails when writing:

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member this.CreateWall (x, y) = 
   (new Rectangle (x, y, this.gridSize, this.gridSize), this.mouseDirection)


with the error messages:
- The method or object constructor CreateWall takes 2 arguments but is here supplied with 1.
- The required signature is member BounceControl.CreateWall : x:'a * y:'b -> 'c.

Isn't it (or shouldn't it be) possible to expand the parameter as has been in OCaml?
(I understand there might be a problem with viewing parameter lists as tuples
and then returning such tuples in other methods)

.

Tupled arguments and multiple arguments are not equivalent for .NET object model members. This also applies to F# object model members. This is because resolving .NET method overloading regularly requires the use of numbers of arguments as part of the resolution.

You can use

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type Point = Point of int * int
    member this.CreateWall(Point(x,y)) = ...

or write

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member this.CreateWall point = 
    let (x,y) = point 
     ...

This does break with OCaml convention but is also a key design decision to ensure that .NET libraries that make heavy use of overloading (i.e. just about every use of a .NET library) are palatable to use from F# and give good error messages when things go wrong.

Kind regards

Don

By on 11/14/2007 6:20 AM ()

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