Logical const

[bearophile]

Walter:

> You can write memoized functions in D, you just can't label them as const.
> You'll be relying on convention. Memoized (logically const) functions are not
> verifiable in C++, either, so you are not technically worse off.

I agree with what you say about C++ here. But in theory it's possible to define a built-in @memoize that's usable on strongly pure functions (and const member functions that are strongly pure), that keeps them strongly pure. In some functional languages this memoization is automatic, but in D it's probably better to keep it on request, as CTFE.

A pure memoized function is useful because you may call it from another pure function, and because pure functions work well with immutability (so you are able to assign to an immutable variable even the result of a memoized strongly pure function).

Bye,
bearophile