Meaning of pure member function

Jesse Phillips jessekphillips+D at
Mon Jan 16 21:40:15 PST 2012

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:

Or stackoverflow:

> 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.

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