Type Annotations

You can provide a type annotation when you declare a constant, to be clear about the kind of values the constant can store

import Cocoa

let constB:Float = 3.14159

let constc:Int = 3.14159// double is not allowed here 

println(constB)

println(constc)

produces following error 

main.swift:6:18: error: 'Double' is not convertible to 'Int'
let constc:Int = 3.14159