Map Purity

[Xinok via Digitalmars-d-learn]

On Sunday, 28 June 2015 at 15:55:51 UTC, jmh530 wrote:
> My understanding of pure is that a function labeled pure can 
> only include pure functions. I've been confused by the fact 
> that a function calling map (like below) can be labeled pure 
> without any problems. The only way I can rationalize it is that 
> map really isn't a function, it's (if I'm understanding it 
> correctly) a template that creates a template function that 
> calls a struct template.
>
> auto test_map(T)(T x) pure
> {
> 	return x.map!(a => a + a);
> }
>
> This is related to
> http://forum.dlang.org/thread/ppmokalxdgtszzllzorb@forum.dlang.org?page=1
> but maybe my question is more basic.

Map isn't explicitly marked as pure. D can infer purity for 
templated functions, so as long as you give it a pure predicate, 
map can be inferred as pure. This only works for templated 
functions; non-templated functions must be explicitly marked as 
pure.