Annex C (informative) Compatibility [diff]

C.3 C++ and ISO C++ 2017 [diff.cpp17]

C.3.8 [temp]: templates [diff.cpp17.temp]

Affected subclause: [temp.names]
Change: An unqualified-id that is followed by a < and for which name lookup finds nothing or finds a function will be treated as a template-name in order to potentially cause argument-dependent lookup to be performed.

Rationale: It was problematic to call a function template with an explicit template argument list via argument-dependent lookup because of the need to have a template with the same name visible via normal lookup.

Effect on original feature: Previously valid code that uses a function name as the left operand of a < operator would become ill-formed.
For example: struct A {}; bool operator<(void (*fp)(), A); void f() {} int main() { A a; f < a; // ill-formed; previously well-formed (f) < a; // still well-formed }