Ambiguity between function and function in namespace with same argument

10

Can anybody explain why there is an ambiguity between A::f(const B& b) and f(const A::B& b). I consider the code to be quite explicit about the intention.

#include <iostream>

namespace A
{
  class B
  {
  protected:
    double value_;
  public:
    B() : value_(15.0) {}
    double getValue() const {return value_;}
  };

  void f(const B& b)
  {
    std::cout << "f(b) = " << b.getValue() << std::endl;
  }
}

void f(const A::B& b)
{
  std::cout << "Other f(b) = " << b.getValue() << std::endl;
}

int main()
{
  A::B b;
  A::f(b);
  f(b);
  return 0;
}

However, both g++ 7.5.0 and clang 6.0.0 complain about ambiguous function call (error: call of overloaded ‘f(A::B&)’ is ambiguous) regardless of compiler flags and optimizations.

c++ namespaces function-call argument-dependent-lookup

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edited 7 hours ago

cigien

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  Another day, another victim of ADL – Yksisarvinen 16 hours ago

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