Nicer syntax for ternary with a let?

Question

Is there a nicer way to do the assignment to DEF in the following example? I want to convert type A to Type B, but still preserve the nil possibility whenever I can.

Can't seem to stumble into a better way of doing this, however. Suggestions?

class ABC {

  var DEF: Int?

  func X (someValue: Int8?) {
    DEF = someValue != nil ? Int(someValue) : nil
  }
}

you might find [this list of ways to handle optionals](http://stackoverflow.com/questions/29717210/when-should-i-compare-an-optional-value-to-nil/29717211#29717211) useful — Airspeed Velocity, Jul 06 '15 at 13:34

oisdk · Accepted Answer · 2015-07-06T13:00:39.163

2

Swift 1:

class ABC {

  var DEF: Int?

  func X (someValue: Int8?) {
    DEF = someValue.map{Int($0)}
  }
}

Swift 2:

class ABC {

  var DEF: Int?

  func X (someValue: Int8?) {
    DEF = someValue.map(Int.init)
  }
}

map() takes an optional, unwraps it, and applies a function to it. If the optional resolves to nil, map() returns nil.

edited Jul 06 '15 at 13:00

answered Jul 06 '15 at 12:55

oisdk

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Airspeed Velocity · Answer 2 · 2015-07-06T13:04:06.977

You are describing optional map:

var i: Int? = 2
let j = i.map { $0 * 2 }  // j = .Some(4)
i = nil
let k = i.map { $0 * 2 }  // k = nil

Think of this map like array or other collection map, where optionals are collections that have either zero (nil) or one (non-nil) element.

Note, if the operation you want to perform itself returns an optional, you need flatMap to avoid getting a double-optional:

let s: String? = "2"
let i = s.map { Int($0) }      // i will be an Int??
let j = s.flatMap { Int($0) }  // flattens to Int?

Nicer syntax for ternary with a let?

2 Answers2