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[Issue 17080] Can assign member-function-ptr to free-function-ptr
[Issue 17080] Can assign delegate to function
Jan 09, 2017
Marenz
Jan 10, 2017
Ketmar Dark
Jan 11, 2017
Sprink
Jan 11, 2017
Marenz
Jan 11, 2017
Sprink
Jan 13, 2017
Dicebot
Jan 13, 2017
Dicebot
Jan 16, 2017
Sprink
Jan 16, 2017
Dicebot
Jan 16, 2017
Sprink
Jul 02, 2017
Vladimir Panteleev
Dec 05, 2017
Mike Franklin
Aug 07, 2019
Simen Kjaeraas
Jan 09
Bolpat
January 09, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

--- Comment #1 from Marenz <dlang@supradigital.org> ---
Note that this not only compiles but also does something very nasty if you call the resulting func. So this silently corrupts your memory which I consider quite dangerous.

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January 10, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

Ketmar Dark <ketmar@ketmar.no-ip.org> changed:

           What    |Removed                     |Added
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                 CC|                            |ketmar@ketmar.no-ip.org

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January 11, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

uplink.coder@googlemail.com changed:

           What    |Removed                     |Added
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           Keywords|                            |accepts-invalid
                 CC|                            |uplink.coder@googlemail.com
            Summary|Can assign delegate to      |Can assign
                   |function                    |member-function-ptr to
                   |                            |free-function-ptr

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January 11, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

Sprink <sprink.noreply@gmail.com> changed:

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
                 CC|                            |sprink.noreply@gmail.com
         Resolution|---                         |DUPLICATE

--- Comment #2 from Sprink <sprink.noreply@gmail.com> ---


*** This issue has been marked as a duplicate of issue 3720 ***

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January 11, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

Marenz <dlang@supradigital.org> changed:

           What    |Removed                     |Added
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             Status|RESOLVED                    |REOPENED
         Resolution|DUPLICATE                   |---

--- Comment #3 from Marenz <dlang@supradigital.org> ---
I have been encouraged by Uplink|DMD to reopen this issue as it differs in a few aspects to the one it is marked a duplicate of:

The issue 3720 should still compile because there isn't anything wrong with taking the address of a delegate, even without the instance (it would simply have .this (or whatever the name is) set to null.

My example however shows an implicit conversion from function -> delegate and that should in no case compile.

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January 11, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

--- Comment #4 from Sprink <sprink.noreply@gmail.com> ---
(In reply to Marenz from comment #3)
> I have been encouraged by Uplink|DMD to reopen this issue as it differs in a few aspects to the one it is marked a duplicate of:
> 
> The issue 3720 should still compile because there isn't anything wrong with taking the address of a delegate, even without the instance (it would simply have .this (or whatever the name is) set to null.
> 
> My example however shows an implicit conversion from function -> delegate and that should in no case compile.

It is the same issue. If issue 3720 is fixed, then this issue wouldn't exist.

    auto fp = &S.fun;
    fp();

This is not valid code and only works because "auto" evaluates to a function. The use case for taking a pointer of a member function is to use it with objects, thus a delegate isn't suited here either.


    auto fp = &S.fun; // this line would need to stay the same

Now it's a matter how to call it? C++ uses a different syntax.

    S s;
    (s.*fp)();

In either case it is the exact same problem, that taking the address of a member function without an instance of that object results in the type being a regular function pointer.

It's not an implicit conversion from function -> delegate, the compiler incorrectly defines it as a function.

    writeln(typeof(fp).stringof); // prints void function(), not delegate

A bunch of other issues that illustrate the same thing are also marked
duplicates.
https://issues.dlang.org/show_bug.cgi?id=12154
https://issues.dlang.org/show_bug.cgi?id=12773

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January 13, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

Dicebot <public@dicebot.lv> changed:

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

--- Comment #5 from Dicebot <public@dicebot.lv> ---
(In reply to Sprink from comment #4)
> It is the same issue. If issue 3720 is fixed, then this issue wouldn't exist.

It is related to 3720 but, contrary to 3720, it can be fixed by simply typing `&S.fun` as a delegate (with null context ptr). Fixing 3720 as a whole is much more delicate matter which I'd prefer to not touch at this context.

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January 13, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

uplink.coder@googlemail.com changed:

           What    |Removed                     |Added
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           Assignee|nobody@puremagic.com        |uplink.coder@googlemail.com

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January 13, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

--- Comment #6 from uplink.coder@googlemail.com ---
I am going to take care of this.
I might take a while though.

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January 13, 2017
https://issues.dlang.org/show_bug.cgi?id=17080

--- Comment #7 from Dicebot <public@dicebot.lv> ---
(In reply to uplink.coder from comment #6)
> I am going to take care of this.
> I might take a while though.

FYI, this is quick hack I figured out after initial investigation that turns `addrOf` result into delegate:

diff --git a/src/expression.d b/src/expression.d
index 041ca86ef..0746d51df 100644
--- a/src/expression.d
+++ b/src/expression.d
@@ -10737,6 +10737,11 @@ extern (C++) final class AddrExp : UnaExp
                             error("'this' reference necessary to take address
of member %s in @safe function %s", f.toChars(), sc.func.toChars());
                         }
                     }
+
+                    Expression ethis = new NullExp(loc,
f.toAliasFunc().vthis.type);
+                    Expression e = new DelegateExp(loc, ethis, f,
ve.hasOverloads);
+                    e = e.semantic(sc);
+                    return e;
                 }
             }
         }

Haven't checked how it affects other code gen though.

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