[LLVMbugs] [Bug 10983] New: -Wunused-parameter should not warn about virtual method declarations with bodies

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Wed Sep 21 21:29:50 PDT 2011


           Summary: -Wunused-parameter should not warn about virtual
                    method declarations with bodies
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: miles at gnu.org
                CC: llvmbugs at cs.uiuc.edu, dgregor at apple.com

In the following code:

   struct X { virtual void f (int a) { } };

One gets a warning from -Wunused-parameter, "unused parameter 'a'".

While this is understandable, I think it's undesirable -- clearly the parameter
'a' will often be used by overrides of X::f, and the parameter name 'a' serves
a valuable documentation purpose here, even if it's not strictly required.

The basic problem of course, is that in this case, f is both a virtual method
declaration which covers overriding methods as well, and a definition of X's
definition of it.

One can avoid this by defining X::f outside the class definition, but for
trivial definitions like the above, this would seem like annoying make-work if
done only to shut up -Wunused-parameter.

My current method of avoiding the warning is to comment out the parameter name: 

   virtual void f (int /* a */) { }

but this again seems like an annoying wart, rather than natural code -- it's
both less readable (especially when the parameter has a funny type like a
function pointer) and yields a slightly confusing inconsistency ("why do you
comment-out some method parameter names but not others?!" "oh it's just to shut
up -Wunused-parameter... :(").

Anyway, the current behavior seems wrong to me; I think -Wunused-parameter
should stay silent for method virtual definitions inside the class definition.

[If this were a very rare scenario, I suppose I wouldn't care about the need to
work around it, but it seems to happen all the time for me...]



p.s. gcc does the same thing; I just posted an identical bug to gcc's bugzilla
... :]

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