swift2 - Swift 2.0: Protocol extensions: Two protocols with the same function signature compile error -

given 2 protocols , extensions:

protocol firstdelegate {     func somefunc() }  protocol seconddelegate {     func somefunc() }  extension firstdelegate {     func somefunc() {         print("first delegate")     } }  extension seconddelegate {     func somefunc() {         print("second delegate")     } } 

and trying conform both of them:

class someclass: firstdelegate, seconddelegate {} 

i receive compile-time error:

type 'someclass' not conform protocol 'firstdelegate'

exchanging firstdelegate , seconddelegate:

class someclass: seconddelegate, firstdelegate {} 

produces reverse:

type 'someclass' not conform protocol 'seconddelegate'

removing 1 of extensions resolves problem. ditto providing implementation somefunc() inside someclass.

this protocol extension functionality rather new me. information in apple's official 'swift programming guide (prerelease)' scarce @ moment.

did violate rules of protocol extensions here?

a protocol defines requirements (methods, properties, ...) conformant type.

protocol firstdelegate {     func somefunc() }  protocol seconddelegate {     func somefunc() } 

defines 2 protocols same required method somefunc(). conformant type must implement method:

class someclass: firstdelegate, seconddelegate {     func somefunc() {         print("someclass implementation")     } } 

a protocol extension provides method , property implementations conformant types. special case of protocol extension default implementation, defined here:

extension firstdelegate {     func somefunc() {         print("first delegate")     } } 

it defines default implementation of somefunc() types conforming firstdelegate. since only required method of protocol, conforming class need not define method @ all:

class someclass: firstdelegate {  }  someclass().somefunc() // output: first delegate 

but if class provides own implementation used:

class someclass: firstdelegate {     func somefunc() {         print("someclass implementation")     } }  someclass().somefunc() // output: someclass implementation 

in case, have defined default implementations of somefunc() both protocols:

extension firstdelegate {     func somefunc() {         print("first delegate")     } }  extension seconddelegate {     func somefunc() {         print("second delegate")     } } 

a class can still conform both protocols if provides own implementation of required method:

class someclass: firstdelegate, seconddelegate {     func somefunc() {         print("someclass implementation")     } } 

but class cannot conform using default implementation

class someclass: firstdelegate, seconddelegate {  } 

for both protocols because there conflict. unspecified default implementation should used, , that's why compiler complains.

actually class conforms none of protocols. can seen in full compiler log in report navigator:

 main.swift:24:7: error: type 'someclass' not conform protocol 'firstdelegate' class someclass: firstdelegate, seconddelegate {       ^ main.swift:5:10: note: multiple matching functions named 'somefunc()' type '() -> ()'     func somefunc()          ^ main.swift:19:10: note: candidate matches     func somefunc() {          ^ main.swift:13:10: note: candidate matches     func somefunc() {          ^ main.swift:24:7: error: type 'someclass' not conform protocol 'seconddelegate' class someclass: firstdelegate, seconddelegate {       ^ main.swift:9:10: note: multiple matching functions named 'somefunc()' type '() -> ()'     func somefunc()          ^ main.swift:19:10: note: candidate matches     func somefunc() {          ^ main.swift:13:10: note: candidate matches     func somefunc() {          ^