Initializing immutable structures is a source of constant grief. Anything
non-trivial requires instancing a mutable structure, initializing it, and
then either casting to immutable (it's up to you to ensure no alias
leaked) or, not to violate the type system, duplicate the whole.
Yet, if there was a situation where the alias leaking is under control,
casting would be safe. Perhaps pure* functions are such a place. They can
only touch the immutable world, whether through globals or through their
parameters. So if one initializes the returned structure with a reference
to the outside world, it will be immutable. And if you stuff the structure
with anything mutable, it must have been created within the function's
body, so no alias leaks.
Call me crazy, but I think it is safe to implicitly convert a pure
function's return value to immutable. What you think?
* here by pure I mean either the old pure** when it still had immutable
arguments, or Don's "immutably pure".
** BTW, http://www.digitalmars.com/d/2.0/function.html still says
immutable, please update.
--
Tomek
- Pure functions as initializers for immutable structur... Tomek Sowiński
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