Swift Protocol Arrays Adding vs. Instantiating -

in swift 3.0 xcode beta 3, defined simple protocol , 2 structs implement it, if initialize array when creating objects, works, if try add elements error:

cannot convert value of type '[h]' expected argument type 'inout _'

shouldn't work?

protocol h {     var v : int { set }     func hello() }  struct j : h {     var v : int     func hello() {         print("j")     } }  struct k : h {     var v : int     func hello() {         print("k")     } }  let ag:[h] =  [k(v:3), j(v:4)] // works ag[0].hello() ag[1].hello()  var af:[h] =  [] af += [k(v:3)] // not work af += [j(v:4)] // not work af[0].hello() af[1].hello() 

it's type issue. need things add af same type af, namely [h]:

var af:[h] = [] let arr1:[h] = [k(v:3)] let arr2:[h] = [j(v:4)] af += arr1 af += arr2