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heterogeneous physical equality for references #7428

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vicuna opened this issue Dec 6, 2016 · 2 comments
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heterogeneous physical equality for references #7428

vicuna opened this issue Dec 6, 2016 · 2 comments
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@gasche
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duplicate feature-wish stdlib

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@vicuna
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vicuna commented Dec 6, 2016

Original bug ID: 7428
Reporter: Christophe Raffalli
Assigned to: @gasche
Status: resolved (set by @gasche on 2016-12-06T18:24:44Z)
Resolution: duplicate
Priority: normal
Severity: feature
Version: 4.04.0
Category: standard library
Duplicate of: #7425

Bug description

I would like the following (or equivalent) to be added somewhere
in the stdlib. This sound type safe and sometimes very useful,
by avoiding a runtime representation of the type.

type ('a,'b) eq = Eq : ('a, 'a) eq | Neq : ('a, 'b) eq

let (===) : type a b.a ref -> b ref -> (a,b) eq = fun r1 r2 ->
if Obj.repr r1 == Obj.repr r2 then Obj.magic Eq else Neq
@vicuna
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vicuna commented Dec 6, 2016

Comment author: @alainfrisch

Do you have some concrete examples where this could be used?

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vicuna commented Dec 6, 2016

Comment author: @gasche

Could we keep discussing this in 7425 where the discussion started? I can rename the other ticket with a more explicit name for the current discussion if you think that is helpful.

#7425

@vicuna vicuna closed this as completed Dec 6, 2016
@vicuna vicuna mentioned this issue Dec 7, 2016
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