When is ADL applied?

Question

There are 3 examples:

I.

typedef int foo;

namespace B
{
    struct S
    {
        operator int(){ return 24; }
    };
        int foo(B::S s){ retu         


        

Answer 1

Your first example does not illustrate ADL. In the line

int t=foo(B::S());

foo is typedefed to int.

The following code has some better illustrations of ADL.

#include 

namespace B
{
    struct S
    {
        operator int(){ return 24; }
    };

    int foo(S s){ return 100; }
    int bar(S s){ return 400; }
}

namespace C
{
    struct S
    {
        operator int(){ return 24; }
    };

    int foo(S s){ return 200; }
}

int bar(C::S s){ return 800; }

int main()
{
    // ADL makes it possible for foo to be resolved to B::foo
    std::cout << foo(B::S()) << std::endl;

    // ADL makes it possible for foo to be resolved to C::foo
    std::cout << foo(C::S()) << std::endl;

    // ADL makes it possible for bar to be resolved to B::bar
    std::cout << bar(B::S()) << std::endl;

    // ADL makes it possible for bar to be resolved to ::bar
    std::cout << bar(C::S()) << std::endl;
}