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Pattern matching allows wildcards to be used with nullary constructors #5502

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vicuna opened this issue Feb 8, 2012 · 2 comments
Closed

Pattern matching allows wildcards to be used with nullary constructors #5502

vicuna opened this issue Feb 8, 2012 · 2 comments
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vicuna commented Feb 8, 2012

Original bug ID: 5502
Reporter: john_nowak
Assigned to: @gasche
Status: closed (set by @xavierleroy on 2013-08-31T10:46:28Z)
Resolution: not a bug
Priority: normal
Severity: minor
Version: 3.12.1
Category: ~DO NOT USE (was: OCaml general)

Bug description

The following should most likely be rejected but are accepted by the compiler:

fun (None _) -> 42
match None with None _ -> 42
...

This bug appears to only be present with wildcards; all other pattern arguments to nullary constructors result in the appropriate error.
@vicuna
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vicuna commented Feb 8, 2012

Comment author: john_nowak

I should note that this is actually a minor portability issue. Older OCaml compilers (e.g. 3.10.2) will reject such code.

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vicuna commented Feb 9, 2012

Comment author: @gasche

This is not a bug but a dubious feature. This behavior is intentional: Foo _ will ignore the constructor at any arity (including zero). This is so you don't have to write eg. Foo (_, _, _, _) if the arity is four, which would be rather painful.

PS: but you can ask to be warned in the case where this construct is used on a constant constructor (arity zero): it's warning 28, introduced in 3.12.0.

@vicuna vicuna closed this as completed Aug 31, 2013
@vicuna vicuna added the bug label Mar 20, 2019
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