arraysswiftset

How type inference works when assuming collection types in swift

var arrayorset=["0","1","21"]

Swift is type inference and type safety but how swift know the difference between the sets and array

it will be the problem when the array is needed instead of a set because sets are unordered list it cannot retrieve me list orderly

so how to solve this problem?

Solution

  • ... how swift know the difference between the sets and array ...

    ["0", "1", "21"]

    is an array literal, and the type inference is documented with the ExpressibleByArrayLiteral protocol (emphasis added):

    Arrays, sets, and option sets all conform to ExpressibleByArrayLiteral
    ...
    Because Array is the default type for an array literal, without writing any other code, you can declare an array with a particular element type by providing one or more values.

    Therefore 

    let arrayOfStrings = ["0", "1", "21"]     // [String]

    declares an array of strings, and an explicit type annotation is needed to declare a set of strings:

    let setOfStrings: Set = ["0", "1", "21"]  // Set<String>

    Note that Set is sufficient for the type annotation here, the element type String is inferred from the array literal.