[swift-evolution] Pure functions

[Daryle Walker]

Should we add support for recognition of pure functions?  These functions don’t refer to any global state; their return values / outgoing in-out parameter states depend solely on the incoming argument values.  I know at least the D programming language acknowledges them.

- Should they be marked with a “pure” attribute?
- How much checking should the complier do on code for purity violations?
- Should purity be a potential requirement on protocol methods?
- What kinds of optimizations are possible?
- What default built-in or standard library support should be pure as an initial set to build your own pure functions?

— 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT mac DOT com 

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