[Issue 4417] New: const-violation in struct error message

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4417

           Summary: const-violation in struct error message
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: diagnostic
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2010-07-02 05:31:17 PDT ---
This D2 program is wrong, because the rnd field of Foo must change its state,
so it can't be called in a const method bar():


import std.random: MinstdRand, uniform;
struct Foo {
    MinstdRand rnd;
    int bar() const {
        return uniform(0, 10, rnd);
    }
}
void main() {}


But dmd v2.047 shows bad error messages:

...\dmd\src\phobos\std\random.d(684): Error: function
std.random.LinearCongruentialEngine!(uint,48271,0,2147483647).LinearCongruentialEngine.front
() is not callable using argument types ()
...\dmd\src\phobos\std\random.d(685): Error: function
std.random.LinearCongruentialEngine!(uint,48271,0,2147483647).LinearCongruentialEngine.popFront
() is not callable using argument types ()
...\dmd\src\phobos\std\random.d(5): Error: template instance
std.random.uniform!("[)",int,int,const(LinearCongruentialEngine!(uint,48271,0,2147483647)))
error instantiating


A better single error message can just say that uniform(_, _, rnd) can't be
called inside bar() because uniform() tries to mutates rnd while bar is const.

See also bug 4416

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