[Issue 5121] New: Make std.algorithm.swap weakly pure

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=5121

           Summary: Make std.algorithm.swap weakly pure
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: patch
          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 2010-10-26 12:57:01 PDT ---
This is a test program that fails with dmd 2.050alpha:


import std.algorithm: swap;
pure int foo(int x, int y) {
    swap(x, y);
    return y;
}
void main() {
    assert(foo(10, 20) == 10);
}


But swap may be modified to become weakly pure, just changing this line 1063:

void swap(T)(ref T a, ref T b) if (!is(typeof(T.init.proxySwap(T.init))))


Into:

pure void swap(T)(ref T a, ref T b) if (!is(typeof(T.init.proxySwap(T.init))))


(Probably several other functions in Phobos may now be tagged was (weakly)
pure.)

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