why Hashtbl.t are not covarint?

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* why Hashtbl.t are not covarint?
@ 2009-01-14  8:02 Radzevich Belevich
  2009-01-14  8:54 ` [Caml-list] " Stéphane Glondu
  0 siblings, 1 reply; 2+ messages in thread
From: Radzevich Belevich @ 2009-01-14  8:02 UTC (permalink / raw)
  To: Caml List

hashtbl.mli: type ('a,'b) t
Why not "type ('a,+'b) t"?


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [Caml-list] why Hashtbl.t are not covarint?
  2009-01-14  8:02 why Hashtbl.t are not covarint? Radzevich Belevich
@ 2009-01-14  8:54 ` Stéphane Glondu
  0 siblings, 0 replies; 2+ messages in thread
From: Stéphane Glondu @ 2009-01-14  8:54 UTC (permalink / raw)
  To: Radzevich Belevich; +Cc: Caml List

Radzevich Belevich a écrit :
> hashtbl.mli: type ('a,'b) t
> Why not "type ('a,+'b) t"?

For the same reason as 'a in 'a ref, i.e. mutable things cannot be
covariant.


Cheers,

-- 
Stéphane


^ permalink raw reply	[flat|nested] 2+ messages in thread

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