[Issue 7587] New: reduce() of a const array of tuples too

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=7587

           Summary: reduce() of a const array of tuples too
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: rejects-valid
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2012-02-25 10:09:28 PST ---
import std.algorithm, std.typecons;
int add1(int x, int y) {
    return x + y;
}
alias Tuple!int T;
T add2(T x, T y) {
    return T(x[0] + y[0]);
}
void main() {
    T[] items1 = [T(0), T(1)];
    const t0 = T(0);
    immutable r1 = reduce!add2(t0, items1); // OK
    const(int[]) items2 = [0, 1];
    const int zero = 0;
    immutable r2 = reduce!add1(zero, items2); // OK
    const(T[]) items3 = items1.idup;
    immutable r3 = reduce!add2(t0, items3); // Error
}



DMD 2.059head gives:

...\dmd2\src\phobos\std\typecons.d(399): Error: template
std.typecons.Tuple!(int).Tuple.opAssign(R) if (isTuple!(R) &&
allSatisfy!(isIdentityAssignable,Types)) does not match any function template
declaration
...\dmd2\src\phobos\std\typecons.d(399): Error: template
std.typecons.Tuple!(int).Tuple.opAssign(R) if (isTuple!(R) &&
allSatisfy!(isIdentityAssignable,Types)) cannot deduce template function from
argument types !()(const(int))
...\dmd2\src\phobos\std\algorithm.d(702): Error: template instance
std.typecons.Tuple!(Tuple!(int)).Tuple.__ctor!(const(Tuple!(int))) error
instantiating
test.d(17):        instantiated from here:
reduce!(const(Tuple!(int)),const(Tuple!(int)[]))
test.d(17): Error: template instance
std.algorithm.reduce!(add2).reduce!(const(Tuple!(int)),const(Tuple!(int)[]))
error instantiating


I think just as reduce works on an const(int[]) it should also work on an
const(Tuple!(int)[]).

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