[Vala] Why no functions returning lists in libgee?

[Martin DeMello <martindemello gmail com>]

How come libgee doesn't have any functions that return new lists (in
particular list.map() and list.filter())? Is it to avoid allocation?
I've been looking at porting ruby's Enumerable module to vala, but I
thought I'd check first as to why it isn't there already, and if this
sort of thing is for some reason a bad idea.

martin