> This is an idea to patch that hole a little, doing this inside pure functions:
> 1) Keep disallowing alloca()/malloc()/etc calls;
> 2) Disallow struct allocations;
> 3) Keep allowing object and dynamic array allocations;
> 4) Disallow read and write of the "ptr" fields of dynamic arrays;
> 5) Disallow casts of object references to something else.

Note this is about _inside pure functions_.

A safer idea comes from using the type system, but it's hard. The idea is introducing "pure memory references". Any memory allocation inside a pure function returns a pointer/reference that can't be _read_ (as value) inside the pure function itself, or even outside it, if it among the function results. I think it's possible to design a type system able to enforce this safely, but I don't think this will happen for D.

Bye,
bearophile

> A safer idea comes from using the type system, but it's hard. The idea is introducing "pure memory references".

I think I have just invented the idea of referentially transparent pointers/references for D, a subtype of normal D pointers/references.

Bye,
bearophile