[Ocaml-lib-devel] ExtList set_field

[Nicolas C. <war...@fr...>]

Recently, after the talks of Xavier Leroy on the main ocaml list, it appear
that Obj.set_field is not working so good. Jacques Garrigue looked at the
generated native code and he noticed that the Obj.set_field is doing
additional (useless) operation by testing the block tag for
Double_array_tag. Not only the code is bigger, but there is a (very) little
speed issue , compared to using a mutable structure like :
type 'a mutlist = { h : 'a ; mutable tl : 'a mutlist; }
I might then modify ExtList soon to clean theses things.
( please note that we still Obj.magic to convert from/to 'a list.

Another problem might come from the "trick" :
let x = [ Obj.magic () ] in
....
List.tl x
who might get outlined by the compiler and thus will be shared by several
calls (which is not what we want since we're muting the tail !). A
workaround is not to use unit but one of the arguments of the function to
prevent to compiler to mark the block as constant.

Nicolas Cannasse