[Issue 10079] New: Builit-in generated opAssign should be pure nothrow @safe in default

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=10079

           Summary: Builit-in generated opAssign should be pure nothrow
                    @safe in default
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: k.hara.pg at gmail.com


--- Comment #0 from Kenji Hara <k.hara.pg at gmail.com> 2013-05-13 20:49:44 PDT ---
If a struct has postblit or destructor, assignment is automatically implemented
with swap-and -destroy..

struct S {
    this(this) {}   // or ~this()
}
void main() {
    S s1, s2;
    s1 = s2;   // is equivalent to
    // auto tmp = s2   // bitwise copy
    // swap(s1, tmp);  // bitwise swap
    // destroy tmp;    // destroy old state of s1
}

The bitwise copy and swap are pure, nothrow and @safe. But currently this code
doesn't work.

struct S {
    this(this) pure nothrow @safe {}
    // and/or ~this() pure nothrow @safe {}
}
void main() pure nothrow @safe {
    S s1, s2;
    s1 = s2;
}

test.d(7): Error: pure function 'D main' cannot call impure function
'test.S.opAssign'
test.d(7): Error: safe function 'D main' cannot call system function
'test.S.opAssign'
test.d(7): Error: s1.opAssign is not nothrow
test.d(5): Error: function D main 'main' is nothrow yet may throw

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