Follow along at https://www.hackingwithswift.com/100/1
Swift variables are initialized with var and hold a value. Pretty straightforward.
But to me, it's useful to know how the language handles mutablity and type inference.
Variables can have their value changed at any later point, as long as the value is of the same type, and they can even be declared without a value so long as we're explicit about the type:
var name: String
var age = 0
name = "Brian"
name = "Roger"
age = 10
age += 1Constants, on the other hand cannot be changed later. To distinguish them from variables, constants are initialized with the let keyword.
While it might seem trivial, this separation is tremendously useful. It allows our code to convey more information about how we intend to use each value. We can "let" things be constant by default, and conservatively use var when needed — specifically because the value held by this variable will be changed later on.
Type inference can be explicit or left up the compiler. I like this because it offers the flexibility of being explicit when you need to, being implicit otherwise — and knowing that the compiler has your back in either case.
Doubles and Ints can be mixed in an expression when they're raw values. The Int will be "upcasted" to avoid information loss:
print(993.1 + 1) // prints 994.1Mixing types in an expression won't work with variables or constants, however:
let pi = 3.141592653589793
let oneHundred = 100
var price = 100.0
var shares = 22
print(pi + oneHundred) // error
print(price * shares) // errorConditional if/else statements have to use actual Booleans, as does the initialization of Booleans. You can take your unnecessary ambiguity and "truthiness" elsewhere 😛.