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tuple lookup
f#

Wow. Four threads in under 24 hours. I should get some kind of trophy for "most ridiculously basic questions asked".

With lists and arrays, I can get an element at a specified index easily. Something like a.[0] works like a charm. Is it possible to do the same thing with a tuple? If I've got a tuple of type "int * int", for instance, I'd like to be able to do something like this:

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let tuple a b = (a, b)

let someFunc =
    let mutable x = 0;
    let mutable y = 0;
    ...
    x, y <- tuple 1 2;
    ...

My desire is to come away from that with x equal to 1 and y equal to 2, but that's not happening.

The error I'm getting is almost the exact opposite of a problem I asked about earlier:
"This expression should have type 'unit', but has type 'float * unit'". I can decompose the tuple with pattern matching, but that feels wrong somehow.

DC

.

I believe the problem here is what you want the <- to do is just not possible. It's designed to update one mutable variable/member at a time, not tuples of them. There's fst and snd functions that can be used to pull tuples apart, I think using them and spreading the operation over two line is your best bet.

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#light
let someFunc() =
    let mutable x = 0
    let mutable y = 0
    let t = (1,2)
    x <- fst t
    y <- snd t
By on 7/26/2007 12:43 AM ()

That's perfectly fine with me. Thanks.

DC

By on 7/26/2007 6:13 AM ()

If you do these assignments within a function, you need not care about using mutable variables and could use the following instead...

(Note that in the global scope this would raise an error because of a duplicate definition)

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#light

let tuple a b = (a, b)
let _ =
    let a, b = tuple 1 2
    //...
    let a, b = tuple 6 9
    print_any a
    print_any b
By on 7/26/2007 9:56 AM ()

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