[LLVMbugs] [Bug 12857] New: Clang should warn about misleading use of pointer-to-member call

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12857

             Bug #: 12857
           Summary: Clang should warn about misleading use of
                    pointer-to-member call
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: jyasskin at google.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


We ran into code like the following:

struct Base {virtual int Foo() {return 0;}};
struct Derived : Base {virtual int Foo() {return 1;}};
int bar(Base* b) {
  return (static_cast<Derived*>(b)->*(&Derived::Foo))();
}

// From here is for illustration:
#include <iostream>
struct MoreDerived : Derived { virtual int Foo() {return 2;}};
int main() {
  MoreDerived d;
  std::cout << bar(&d) << '\n';
}


The author of bar() intended to avoid virtual call overhead in calling
Derived::Foo. However, the syntax he used actually behaves the same as
"static_cast<Derived*>(b)->Foo()" and results in "2". The syntax he wanted was
"static_cast<Derived*>(b)->Derived::Foo()", which results in "1".

It would be nice if clang would warn about calling through a literal
pointer-to-member, with fixits suggesting the two shorter forms.

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