6.2 The Basic Assignment Operator
We have already looked at the most basic of assignment operators, the = operator. This assignment operator simply assigns the result of an expression to a variable. In essence, the = assignment operator takes two operands. The left-hand operand is the variable or constant to which a value is to be assigned and the right-hand operand is the value to be assigned. The right-hand operand is, more often than not, an expression which performs some type of arithmetic or logical evaluation, the result of which will be assigned to the variable or constant. The following examples are all valid uses of the assignment operator:
var x: Int? // Declare an optional Int variable
var y = 10 // Declare and initialize a second Int variable
x = 10 // Assign a value to x
x = x! + y // Assign the result of x + y to x