Re: Calling dynamically bound functions from weakly pure function

[Rene Zwanenburg via Digitalmars-d-learn]

On Saturday, 19 July 2014 at 11:12:00 UTC, Marc Schütz wrote:
Casting to pure would break purity if the called function is 
not actually pure. AFAIU, the problem is that the mutable 
function pointers are not accessible from inside the pure 
function at all, in which case the solution is to cast them to 
immutable, not to pure.

Indeed that is the problem. I didn't think of casting to 
immutable, that should work..


But to cast something, you'd need to have access to it in the 
first place...

This seems to work:

    int function(int) pure my_func_ptr;

    struct CallImmutable {
        static opDispatch(string fn, Args...)(Args args) {
            return mixin(fn)(args);
        }
    }

    int test() pure {
        return CallImmutable.my_func_ptr(1);
    }

But I suspect it's because of a bug. `CallImmutable.opDispatch` 
should not be deduced to be pure, and this not be callable from 
`test`.

Yeah that looks like a bug. I should be able to conjure something 
up, perhaps using assumeUnique, that won't break in newer 
versions.

Thanks for the answers!