Question

Is this valid under the recently updated standard?

auto main = [](int argc, char* argv[]) -> int
{
    return 0;
};

My best guess is that it depends on whether main() MUST be a function, or if it is allowed to be any globally scoped symbol that is callable (with ()).

Answer 1

No, and here’s why:

[n3290: 3.6.1/1]: A program shall contain a global function called
main, which is the designated start of the program. It is
implementation-defined whether a program in a freestanding environment
is required to define a main function. [ Note: In a freestanding
environment, start-up and termination is implementation-defined;
startup contains the execution of constructors for objects of
namespace scope with static storage duration; termination contains the
execution of destructors for objects with static storage duration.
—end note ]

Lambdas are not functions, but function objects or functors:

[n3290: 5.1.2/3]: The type of the lambda-expression (which is
also the type of the closure object) is a unique, unnamed nonunion
class type — called the closure type — whose properties are described below. [..]