fileExtension

auto app_d = FileName("app.d");
assert( app_d.matchFirst(fileExtension("d")));
assert(!app_d.matchFirst(fileExtension("c")));
assert(!app_d.matchFirst(fileExtension("cpp")));
auto app = FileName("app");
assert(!app.matchFirst(fileExtension("d")));
assert(!app.matchFirst(fileExtension("c")));
assert(!app.matchFirst(fileExtension("cpp")));
auto app_c = FileName("app.c");
assert(!app_c.matchFirst(fileExtension("d")));
assert( app_c.matchFirst(fileExtension("c")));
assert(!app_c.matchFirst(fileExtension("cpp")));