Meaning of pure member function

[Jesse Phillips]

On Tuesday, 17 January 2012 at 05:16:33 UTC, H. S. Teoh wrote:
> The following code compiles without error:
>
> 	class C {
> 		int x;
>
> 		// what does 'pure void' mean??
> 		pure void f() {
> 			x++;		// why is this legal?
> 		}
> 	}
>
> What does 'pure' mean when applied to a member function?

This is a weakly pure function usable by strongly pure functions. 
Namely it is a helper function to those that can claim to be 
strongly pure.

Maybe bearophile's blog will shed some light:

http://leonardo-m.livejournal.com/99194.html

Or stackoverflow:

http://stackoverflow.com/questions/5812186/pure-functional-programming-in-d

> Furthermore, what on earth is 'pure void' supposed to
> mean and why does the compiler accept it?

Well it can only be useful as a weakly pure function as those are 
allowed to modify their arguments.

In any case, if the function was strongly pure:

pure void foo() {}

any call to it would just be eliminated as having no side effects.