parts/4.3.SymbolLookupResolution.md

Add to clause 4 “Language concepts” an issue on C++ symbol lookup issues considering the following: 1. Minimize the set of names that are available to avoid referring to an item that was not the intended target 2. hidden friends 3. ADL (argument dependent lookup) 4. Lack of this-> in class templates 5. Minimizing lexical scope and visibility 6. Minimizing names in global scopes 7. Minimizing use of “using” directives


namespace NS {
template <typename T>
struct A
{
   template <typename S, typename Q> friend void add (S, Q);
};
}

struct B {
    B(int);
    B (NS::A<int> const &);
};

B & add(B const & lhs, B const & rhs);

void bar (NS::A<int> & a, B const & b)
{
    add(a, b);
}

A C++ program may span multiple scopes, and when a function is called, the compiler may have many choices to select from to resolve the actual function that will be called. The set of names found for a function depend upon whether the name is qualified or if it is unqualified.

Unqualified lookup begins the search in the current scope and works its way out to the global scope and stops when it finds the first matching name. The search will include: - Names directly visible; - (Non-dependent) base classes if the scope is for a member; - Names introduced by the using declaration; - Names introduced by the using directive; and - Members of inline namespaces After these steps, Argument-Dependent Lookup (ADL) occurs. In ADL, the scope(s) of type of the function’s arguments are also searched. This search also includes friends that would not normally be found. ADL never finds member functions.

Unqualified name lookup in templates has two phases: - When the template is initially parsed, names are looked up as above, excluding dependent bases; and - When the template is instantiated, ADL is performed for function names, but ADL does not find member functions.

A qualified name lookup takes place when: - the name includes its scope (e.g a::foo); or - the name is used in a class member access expression (this->foo). Qualified lookup only searches: - Names directly visible; - (Non-dependent) base classes if the scope is for a member; - Names introduced by the using declaration; - Names introduced by the using directive; - Members of inline namespaces; and - Names that can be resolved when a template is instantiated.

4.2 Symbol Lookup and Overload Resolution