Proposal: Relax rules for 'pure'

[sclytrack]

> > So weakly-pure should not access global stuff. But that is harder
> > to track by the compiler with mutable parameters.
> Not really. You just need to disallow shared, __gshared in pure function
> declarations.
> > Or weakly-pure is only noglobal when called in pure routines, because of the
> > immutable barrier.
> > Unwritten contract, not checked by the compiler?  (Like property getters shouldn't
> > modify the "state" of the object.)
> No. The contract is, that the function only has access to the parameters
> you have given it. It depends _only_ on its parameters.
>   If you've made all parameters immutable or value types, it's strongly
> pure.
> These additional contracts come automatically from the type system.


pure doStuff( [immutable] int a, [unshared] MyClass a)
{
}

1) If shared it must be immutable.
2) If mutable it must be not shared.