[Issue 6741] New: implicit casting of pure-function delegate result to immutable breaks immutability.

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6741

           Summary: implicit casting of pure-function delegate result to
                    immutable breaks immutability.
           Product: D
           Version: D2
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: schveiguy at yahoo.com


--- Comment #0 from Steven Schveighoffer <schveiguy at yahoo.com> 2011-09-29 10:46:04 PDT ---
For example:

class A {
    int n;
    void delegate( ) dg;
    void foo() {n++;}
}

pure
A createAnA( int n ) {
    A result = new A;
    result.n = n;
    result.dg = &result.foo;
    return result;
}

void main( ) {
    immutable A tmp = createAnA( 3 );
    assert( tmp.n == 3 );
    tmp.dg();
    assert( tmp.n == 4 );
}

Because delegates cannot be cast, I think it should be illegal to cast a
delegate-containing object or struct to immutable implicitly.  An explicit cast
should be required.

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