[Issue 1983] New: Big Hole in Const System

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=1983

           Summary: Big Hole in Const System
           Product: D
           Version: 2.012
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: caron800 at googlemail.com


There appears to be a large hole in the const system, demonstrated by the
following code.

    import std.stdio;

    class A
    {
        private int x_ = 1;
        void x(int n) { x_ = n; }
        int x() const { return x_; }
    }

    void main()
    {
        const(A) a = new A;

        // The following correctly won't compile
        // a.x = 2;
        // a.x(2);

        // **** BUT THIS WILL ****
        (&a.x)(2);

        writefln(a.x); // writes 2
    }

The problem is that the expression (&a.x) has type

    void delegate(int x)

wheras it /should/ have type

    void delegate(int x) const

Unfortunately, there is no way to declare a const delegate (by which I mean, a
delegate whose context pointer is typed const).

I see this as a big problem. Without the ability to specify the constancy of
delegate contexts, it will be impossible to declare pure delegates. (If we ever
get parallel foreach, we're going to need pure delegates).


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