core.exception.AssertError@prog.d(3): null this
----------------
??:? _d_assert_msg [0x4daa4006]
??:? int prog.S.f() [0x4daa3be3]
??:? _Dmain [0x4daa3bfa]
??:? _D2rt6dmain211_d_run_mainUiPPaPUAAaZiZ6runAllMFZ9__lambda1MFZv [0x4daa4693]
??:? void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).tryExec(scope void delegate()) [0x4daa45bf]
??:? void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).runAll() [0x4daa4638]
??:? void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).tryExec(scope void delegate()) [0x4daa45bf]
??:? _d_run_main [0x4daa4523]
??:? main [0x4daa3c8f]
??:? __libc_start_main [0x4ea762b0]