• "H. S. Teoh" <hsteoh quickfur.ath.cx> Mar 06 2012
• "Adam D. Ruppe" <destructionator gmail.com> Mar 06 2012
• bearophile <bearophileHUGS lycos.com> Mar 06 2012

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

Why is std.algorithm.reduce not marked pure? It makes it impossible to
do things like this:

	pure const int product(int[] args) {
		return reduce!"a * b"(args);
	}


T

-- 
Life is unfair. Ask too much from it, and it may decide you don't deserve what
you have now either.

"Adam D. Ruppe" <destructionator gmail.com> writes:

On Tuesday, 6 March 2012 at 22:39:20 UTC, H. S. Teoh wrote:
 Why is std.algorithm.reduce not marked pure?


It doesn't have to be - templates are inferred to be
pure or not.

If you take the const off that signature, your example
works in today's dmd.

bearophile <bearophileHUGS lycos.com> writes:

H. S. Teoh:

 But why can't 'this' be const? For example, why does the compiler reject
 this:
 
 	class A {
 		int[] data;
 		pure const int sum() {
 			return reduce!"a*b"(data);
 		}
 	}
 
 I'm not modifying data at at all, so why should it be an error?


I think it's a small bug in std.algorithm.reduce, is this in Bugzilla already?


import std.algorithm: reduce;
void main() {
    const data = [2, 3, 4];
    int r1 = reduce!q{a * b}(0, data); // OK
    int r2 = reduce!q{a * b}(data);
}



In std.algorithm.reduce there is also this (now bug 2443 is fixed) at about
line 723:

            // For now, just iterate using ref to avoid unnecessary copying.
            // When Bug 2443 is fixed, this may need to change.
            foreach(ref elem; r)
            {
                if(initialized)

Bye,
bearophile