[swift-evolution] [Pitch] Support for pure functions. Part n + 1.

[Anton Zhilin]

2017-02-17 17:13 GMT+03:00 T.J. Usiyan <griotspeak at gmail.com>:

It is my opinion that you are describing an entirely different, and
> somewhat orthogonal, feature. I would like the feature that you describe.
> Constant expressions are powerful and open up quite a few optimizations.
> What constexpr addresses is not purity, at the heart of it. Pure
> expressions that accept compile-time-known values are, by happy accident,
> compile-time-computable, but pure expressions that accept dynamic values
> are not. Conflating the two qualities of being compile-time-known and being
> pure within the same keyword and overloading it in this way is not
> desirable to me.
>
I see now. I’d say that access to global state is not vital, and @pure
functions are more useful than @const functions, so I’m OK with having only
@const functions.

To control growth of compilation time, we could have both @pure function
annotation and @const variable annotation to *ensure* that a @pure
expression is computed at compilation time.

I’d also want to infer @pure whenever possible, but is it possible with
functions in different modules?
​
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