Published on 13 November 2015 Tweet
Swift is very strongly typed. All variables have a type. There is a type in Swift called optional. Optional can have only two values:
var something = display.text
What type is “something”? We didn’t specify the type of this variable. Swift can infer the type from the context. It makes “something” to be the same type of display.text. Lets say “display.text” is a type of string, then “something” is an optional string, which is an optional that can be a string.
How to get a string from an optional? You can unwrap the optional, meaning you look in there and get the associated value, with an exclamation mark.
var something = display.text!
Now the type of “something” is a string, not an optional anymore. Note that if display.text value is nil, then your program is gonna crash!
Originally published at victorleungtw.com on November 13, 2015.