Identifier.md

Identifier Pattern

Identifier pattern allows to match any value and bind it to a variable or constant through type inference capability. The pattern, as its name suggests, identifies the matched value, infers its type and binds it.

Consider the following example:

var message = "Hello World"

Here, the property message is of type String.

var age = 23

And here the age property is of type Int. We can check this out by getting the Metatype with the help of type(of:) function:

let ageType = type(of: age)
debugPrint("type of age is : ", ageType) // The ageType is Int

We can redefine which type should be considered as the Identifier type for a particular literal type:

typealias IntegerLiteralType = Double

We redefined the default type for Integer type, that is used by default with the Identifier pattern. Now, the already familiar property assignment will produce a slightly different result:

var weight = 89

Except that the type now Double, rather than Int. We can check it out by getting the Metatype:

let weightType = type(of: weight)
debugPrint("type of weight is : ", weightType) // The weight is Double

However, you need to be very careful if you redefine any literal type through typealias, since it may cause some issues that are hard to debug. As a general rule of thumb, try not to touch type literals and if you are not sure about which type will be infered, just make it explicit for the sake of simplicity. Better verbose than sorry 😄.