Exactly Initializer

The init(exactly:) initializer is available on all built-in numeric types in Swift, including Int, Float, Double, UInt, Int8, Int16, Int32, Int64, UInt8, UInt16, UInt32, and UInt64. 

When you use the init(exactly:) initializer, you're essentially telling Swift that you want to create a new instance of a numeric type with a given value, but only if that value can be represented exactly in the given type. If the value cannot be represented exactly, the initializer will return nil. 

For example, consider the following code:

let x = Float(exactly: 1.23)
let y = Float(exactly: 1.23456789)

In this case, x will be initialized with a value of 1.23, since this value can be represented exactly as a Float. However, y will be initialized as nil, since 1.23456789 cannot be represented exactly as a Float.

 Using the init(exactly:) initializer can be useful when you're working with numeric values that need to be accurately represented. For example, if you're working with financial data, you may want to ensure that all calculations are performed with exact values, rather than approximations. In such cases, you can use the init(exactly:) initializer to create instances of numeric types that can represent values exactly, and then perform your calculations with those instances. 

Note that the init(exactly:) initializer is only available in Swift 5.1 and later. If you're using an earlier version of Swift, you'll need to use alternative methods for converting between numeric types.