digitalmars.D.bugs - [Issue 2557] New: inconsistent behavior when taking reference to member without instance
- d-bugmail puremagic.com (25/25) Jan 05 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (6/6) Jan 05 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (17/17) Jan 11 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (7/10) Jan 11 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (5/5) Jan 11 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (5/5) Jan 11 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (20/22) Jan 12 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (6/6) Jan 12 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (11/14) Jan 12 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2557
- d-bugmail puremagic.com (9/10) Jan 14 2009 I understand the difference between "works" and "compiles', it does work...
http://d.puremagic.com/issues/show_bug.cgi?id=2557 Summary: inconsistent behavior when taking reference to member without instance Product: D Version: 1.037 Platform: All OS/Version: All Status: NEW Severity: normal Priority: P2 Component: DMD AssignedTo: bugzilla digitalmars.com ReportedBy: d brian.codekitchen.net See attached test case. When the current context has no 'this', taking a reference to a member function works correctly. However inside another class' instance method, the same code throws an error, seemingly trying to automatically apply the current 'this' even though I'm trying to take a function, not a delegate. The inconsistent behavior is buggy. I would argue towards allowing the reference to be taken in the 'this' instance, since it can be useful when building up delegates as shown in the test case. Obviously pointless here, but I discovered the bug when trying to refactor my code for walking over a collection calling a given method after applying a filtering function, so there is real-world call for doing this. --
Jan 05 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557 Created an attachment (id=285) --> (http://d.puremagic.com/issues/attachment.cgi?id=285&action=view) test case --
Jan 05 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557 smjg iname.com changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |smjg iname.com Keywords| |accepts-invalid It doesn't work. "works" means "behaves correctly", not "compiles without error". The code is wrong regardless of whether dofun is static or not. A.fun needs an object of type A. But it doesn't have one. ---------- bz2557.d(21): Error: this for fun needs to be type A not type method_ref.B bz2557.d(21): Error: cannot implicitly convert expression (&this.fun) of type void delegate() to void function() ---------- --
Jan 11 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557The code is wrong regardless of whether dofun is static or not. A.fun needs an object of type A. But it doesn't have one.I'm not so sure. Object of type A is provided by these two lines of code: A a = new A; dg2.ptr = cast(void*)a; --
Jan 11 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557 But your code tries to use &A.fun, not &a.fun. For &A.fun to make any sense with A being a type, fun would have to be a static method of A. --
Jan 11 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557 That's a feature! Even if method is not static, it still has a single unique body. If so, why can't you take its address? --
Jan 11 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557That's a feature! Even if method is not static, it still has a single unique body. If so, why can't you take its address?http://www.digitalmars.com/d/1.0/type.html#delegates "There are no pointers-to-members in D, but a more useful concept called delegates are supported." Even if there were, the type would not be void function() as is declared in the attached code, but rather void function(A) or perhaps something like void A.function() akin to C++ notation (IIRC) void (A::*)() Maybe void function() would work if the calling convention specifies that the context pointer be always passed in a register that is never used for any other kind of function argument, but that isn't the case in the current ABI. --
Jan 12 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557 Makes sense. Perhaps, another enhancement report should be created with a request to change typeof(&A.foo) from void function() to void delegate() with a dg.ptr being null. --
Jan 12 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557Makes sense. Perhaps, another enhancement report should be created with a request to change typeof(&A.foo) from void function() to void delegate() with a dg.ptr being null.That would still be prone to accidental misuse IMO. Really, D should do one of the following: (a) add method pointer types (b) define &A.foo to be of a type that has the context pointer as just another parameter (which might break if ABI changes to support function-to-delegate conversion are implemented) (c) (continue to) disallow &A.foo altogether --
Jan 12 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2557It doesn't work. "works" means "behaves correctly", not "compiles without error".I understand the difference between "works" and "compiles', it does work in my testing. The method body I'm taking a pointer to is empty in the test case but I first ran into this inconsistency while refactoring some code, where the method body was *not* empty and the code inside the method executed correctly. Whether it *should* work or not is certainly debatable, but I find it a useful behavior except for the inconsistency shown. --
Jan 14 2009