Using Xcode7 beta 6, this little test program:
protocol StringInitializable { init?(_ v: String) }
extension String : StringInitializable { }will make the compiler do this:
$ swiftc test.swift
...
Stack dump:
0. Program arguments: /Applications/Xcode7-beta6.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -c -primary-file test.swift -target x86_64-apple-darwin14.5.0 -enable-objc-interop -sdk /Applications/Xcode7-beta6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk -color-diagnostics -module-name test -o /var/folders/50/br4kxvjd0t551h0fmtrzkwdw0000gn/T/test-4efedc.o
1. While emitting IR SIL function @_TTWSS4test19StringInitializableS_FS0_CuRq_S0__fMq_FSSGSqq__ for 'init' at <invalid loc>
<unknown>:0: error: unable to execute command: Segmentation fault: 11
<unknown>:0: error: swift frontend command failed due to signal (use -v to see invocation)As can be seen in the code, the protocol has a failable initializer and I guess the non-failing but otherwise matching initializer of String trips up the compiler. Perhaps there should be a compile time error for cases like this?