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digitalmars.D.bugs - [Issue 3051] New: Passing alias to member function does not work (1/2)

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3051

           Summary: Passing alias to member function does not work (1/2)
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: andrei metalanguage.com


This is the first of two related bug reports.

class A
{
    A next;

    void fun(alias fun)()
    {
        assert(0);
    }

    void gun()
    {
        void hun(A a)
        {
        }
        next.fun!(hun)();
    }
}

Error: template instance cannot use local 'hun' as parameter to non-global
template fun(alias fun)

This might not work due to an implementation limitation in the current dmd (the
"this" pointer and the stack frame pointer compete for the same register), but
as the next bug will show, the code doesn't work even if said limitation is
worked around.

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Jun 04 2009
next sibling parent d-bugmail puremagic.com writes:
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PDT ---
how on earth templates can be parameterized with values unevaluatable at
compile time?

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Jun 05 2009
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Steven Schveighoffer <schveiguy yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schveiguy yahoo.com





06:17:44 PDT ---
I thought the same as you at first, but I tried this code, and it works:

    void fun(alias fx)()
    {
        fx();
    }

    void main()
    {
        int x = 0;
        void hun()
        {
             x++;
        }
        fun!(hun)();
        writefln("%s", x); // outputs 1
    }

So I think Andrei is right, it is probably a conflict of 2 this pointers
required.  The second bug is legit, as it is equivalent to what I wrote here,
but I think this one is invalid (need 2 this pointers).

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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PDT ---
huh... &fun is a delegate! Does it take stack pointer with all needed
information? Quite hackish, I would say... foreign function messing my stack...
ugh...
So it behaves as nested function, but they are said to access this pointer
through stack, not register.

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08:00:23 PDT ---
Since the template is instantiated differently for each function that it is
called with, it's entirely possible to "know" the stack frame pointer since it
will be a constant offset from the current stack pointer.  I think that is why
it can work.

In fact, I'm now unsure why that can't work in the other bug too...

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08:10:38 PDT ---

 In fact, I'm now unsure why that can't work for both these bugs too...
One other thing about having two "this" pointers, how come this can work (tested with dmd 1.043)? void foo(delegate void() dg) { dg(); } class C { int y; void fun() { int x = 0; void gun() { x++; y++; } // 2 this pointers needed here! foo(&gun); } } So probably there should be no conflict. And the "this" pointer of the alias'd function in the bug's example should be statically calculatable, so it doesn't need to occupy a register. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jun 05 2009
prev sibling next sibling parent d-bugmail puremagic.com writes:
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PDT ---
void foo(delegate void() dg)
{
  dg();
}

class C
{
   int y;
   void fun()
   {
       int x = 0;
       auto me=this;
       void gun()
       { stack.x++; stack.me.y++; }
       foo(&gun); //closure
   }
}

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Jun 10 2009
prev sibling parent d-bugmail puremagic.com writes:
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Dicebot <public dicebot.lv> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |public dicebot.lv



So old and so annoying ;)

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Aug 02 2013