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propapate type disambiguation to the record pattern #7582

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vicuna opened this Issue Jul 11, 2017 · 3 comments

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vicuna commented Jul 11, 2017

Original bug ID: 7582
Reporter: @ygrek
Assigned to: @gasche
Status: resolved (set by @gasche on 2017-07-11T21:13:47Z)
Resolution: duplicate
Priority: normal
Severity: feature
Version: 4.04.1
Category: language features
Duplicate of: #7389

Bug description

Given the following

module T = struct type t = { a : int; b : float } let create a b = { a; b } end;;

(1) Type of the returned value is propagated to the binding and compiler can resolve record fields just fine :

let unwrap () = let x = T.create 1 2. in (x.a,x.b);;

(2) But substituting with record pattern doesn't work :

let unwrap () = let {a;b} = T.create 1 2. in (a,b);;
Error: Unbound record field a

(3) Have to explicitly annotate record type :

let unwrap () = let {T.a;b} = T.create 1 2. in (a,b);;

Seems like a common pattern in code, would be nice to make (2) work?

Additional information

Same behaviour in 4.04.1 and 4.05.0+rc1

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vicuna commented Jul 11, 2017

Comment author: @gasche

I asked the same question in #7389, but it turns out (see discussion there) that it is actually not easy to do this in a general and satisfying way.

@vicuna vicuna closed this Jul 11, 2017

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vicuna commented Jul 11, 2017

Comment author: @ygrek

Thanks, I looked for the duplicate but couldn't find it

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vicuna commented Jul 11, 2017

Comment author: @gasche

Yeah, my title choice was pretty bad. No worries!

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