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[Caml-list] optimizing functors
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Date: -- (:)
From: Xavier Leroy <xavier.leroy@i...>
Subject: Re: [Caml-list] optimizing functors
> OCaml does inlining of functions in the same module. Does it also do it
> between different modules?

Yes, but not across functor applications.  More precisely, functions
that are passed through a functor parameter cannot be inlined nor
called with the optimized "direct" application scheme, they always go
through the generic "indirect-through-closure" application scheme.

> Would it optimize the following:
> 
> module M=
> struct
>   let f = function 0 -> true | _ -> false
> end
> 
> module N (D : sig val f: int->bool end) =
> struct
>   let f = D.f
> end
> 
> module P=N(M)
> 
> Does the compiler optimize the call to f in P, resolving it directly to
> M.f, or does it do multiple indirections?

It will do exactly one indirection: fetch a function closure from P.f (which
happens to be the closure of M.f), and call it indirectly (and without
inlining).  

- Xavier Leroy
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