CompilerCrash.swift

//  MyClass.swift
//  MinimalCrashExample
//
//  Created by Andy Bartholomew on 1/4/16.

import Foundation

class MyStruct {
  var someValue: Int

  init(someValue: Int) {
    self.someValue = someValue
  }
}

protocol SomeProtocol {
  var someValue: Int { get }
  func doSomethingWithValue() -> Int
}

extension SomeProtocol {
//  This method causes a compiler seg fault
  func doSomethingWithValue(secretArg: Int? = nil) -> Int {
    return self.someValue + 1
  }
}

extension MyStruct : SomeProtocol {

}

func test() {
  let myStruct = MyStruct(someValue: 5)
  print(myStruct)
  print(myStruct.doSomethingWithValue())
}

Default arguments in a protocol extension cause the compiler to seg fault in XCode 7.2