Swift Question
concatenate in swift3.0: Binary operator '+' cannot be applied to operands of type '[]' and '[]?'
get the error in Swift3.0:
Binary operator '+' cannot be applied to operands of type '[FutureTrainee]' and '[FutureTrainee]?'
Code:
let newTrainees = data?["data"].arrayValue.map({ (json) in
return FutureTrainee(data: json)
})
let trainees = self.futureTraineeCollection.futureTrainees + newTrainees
Answer Source
Just as the error suggests, you can't use + to add [FutureTrainee] (a.k.a Array<FutureTrainee>) and [FutureTrainee]? (a.k.a. Optional<Array<FutureTrainee>>.
newTrainees has type [FutureTrainee]? because you used optional chaining to subscript data with "data". This code:
let newTrainees = data?["data"].arrayValue.map({ (json) in
return FutureTrainee(data: json)
})
is like:
var newTrainees: [FutureTrainee]?
if let data = data {
newTrainees = data["data"].arrayValue.map({ (json) in
return FutureTrainee(data: json)
})
else {
newTrainees = nil
}
You need to make sure you only append the newTrainees if it's not nil, like so:
var trainees = self.futureTraineeCollection
if let newTrainees = data?["data"].arrayValue.map{ FutureTrainee(data: $0) } {
// If that expression is not nil, the result is bound to "newTrainees"
trainees += newTrainees
}