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Feature Request: mutable local parameters
f#

Now that mutables are allowed everywhere in F# and not just in records like OCaml,
I'd like to propose mutable local parameters to make it consistent.
It's especially handy for implicit constructors with mutable fields so you don't end up duplicating code like this:

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type Test (x : int) =


    let mutable x = x


    member t.Bla y =


        x <- x + y

But I'd like to write this, but this doesn't work:

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type Test (mutable x : int) =


    member t.Bla y =


        x <- x + y

This works but it is not what I intended since with a ref cell the change
doesn't stay local:

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type Test (x : int ref) =


    member t.Bla y =


        x := x + y
.

> ... I'd like to write this, but this doesn't work:

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type Test (mutable x : int) = 
    member t.Bla y = 
        x <- x + y

IMHO, this doesn't seem like a good idea.
If I glanced at the above I would expect that "x" was a local c'tor variable, and would expect its value to disappear after the assignment.

While with:

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type Test (x : int) = 
    let mutable x = x 
    member t.Bla y = 
        x <- x + y

it is obvious that we have a closure around the mutable.

thanks,
mike

By on 5/8/2009 12:20 PM ()

I think that a novice might expect the second option to act like the third option.

By on 5/7/2009 4:39 PM ()

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