> crystal test.cr
Undefined symbols for architecture x86_64:
"std::string::_Rep::_M_destroy(std::allocator<char> const&)", referenced from:
Hello::hello(char const*) in hello.a(libhello.o)
"std::string::_Rep::_S_empty_rep_storage", referenced from:
Hello::hello(char const*) in hello.a(libhello.o)
"std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&)", referenced from:
Hello::hello(char const*) in hello.a(libhello.o)