error output:
main.swift:8:26: warning: will never be executed let hoge: CustomString = "fuga" ^ main.swift:8:26: note: a call to a never-returning function let hoge: CustomString = "fuga" ^ main.swift:4:14: warning: will never be executed self = "hoge" ^ main.swift:4:16: note: a call to a never-returning function self = "hoge" ^ main.swift:3:5: warning: will never be executed init(stringLiteral value: StringLiteralType) { ^ main.swift:3:5: note: a call to a never-returning function init(stringLiteral value: StringLiteralType) { ^ #0 0x0000000003f24d54 PrintStackTraceSignalHandler(void*) (/usr/bin/swift+0x3f24d54) #1 0x0000000003f25096 SignalHandler(int) (/usr/bin/swift+0x3f25096) #2 0x00007f2fb4579390 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x11390) #3 0x00007f2fafce7424 _T0S2SBp21_builtinStringLiteral_Bw17utf8CodeUnitCountBi1_7isASCIItcfC (/usr/lib/swift/linux/libswiftCore.so+0x13c424) #4 0x00007f2fb49a80e4 #5 0x00007f2fb49a80fa #6 0x00007f2fb49a80fa #7 0x00007f2fb49a80fa #8 0x00007f2fb49a80fa #9 0x00007f2fb49a80fa #10 0x00007f2fb49a80fa #11 0x00007f2fb49a80fa #12 0x00007f2fb49a80fa #13 0x00007f2fb49a80fa #14 0x00007f2fb49a80fa #15 0x00007f2fb49a80fa #16 0x00007f2fb49a80fa #17 0x00007f2fb49a80fa #18 0x00007f2fb49a80fa #19 0x00007f2fb49a80fa #20 0x00007f2fb49a80fa #21 0x00007f2fb49a80fa #22 0x00007f2fb49a80fa #23 0x00007f2fb49a80fa #24 0x00007f2fb49a80fa #25 0x00007f2fb49a80fa #26 0x00007f2fb49a80fa #27 0x00007f2fb49a80fa #28 0x00007f2fb49a80fa #29 0x00007f2fb49a80fa #30 0x00007f2fb49a80fa #31 0x00007f2fb49a80fa #32 0x00007f2fb49a80fa #33 0x00007f2fb49a80fa #34 0x00007f2fb49a80fa #35 0x00007f2fb49a80fa #36 0x00007f2fb49a80fa #37 0x00007f2fb49a80fa #38 0x00007f2fb49a80fa #39 0x00007f2fb49a80fa #40 0x00007f2fb49a80fa #41 0x00007f2fb49a80fa #42 0x00007f2fb49a80fa #43 0x00007f2fb49a80fa #44 0x00007f2fb49a80fa #45