ios - Inconsistency in Swift optional protocol behaviour -

coming .net, trying learn swift3/ios , got puzzled following apparent inconsistent behaviour of optional protocol members. suspect got juggling between objc/swift words, missing here actually?

// in playground, given below:  @objc protocol someptotocol {     @objc optional func somemethod() }  class somedelegate: nsobject, someptotocol { }  class somecontroller: nsobject {     var delegate: someptotocol = somedelegate() }  // works , compiles without error  let controller = somecontroller() controller.delegate.somemethod?()      // no error, typed '(() -> ())?'  // fails compile ??  let delegate = somedelegate() delegate.somemethod?()  // error: 'somedelegate' has no member 'somemethod' 

i expect either both fail or both pass, if please enlighten me on anomaly.

the difference between 2 blocks of code type of variable involved.

in first block, delegate explicitly typed someptotocol, , protocol defines somemethod method, statement valid.

in second block, delegate implicitly typed somedelegate , although class conforms someptotocol, doesn't implement optional method somemethod, error.

if change second block

let delegate: someptotocol = somedelegate() delegate.somemethod?() 

which equivalent first block, there no error.