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This tutorial belongs to the Swift series
Think about this expression:
let amount = 1 + 2 * 3The value of amount could change drastically depending on whether 1 + 2 is calculated before 2 * 3.
The order of calculation is determined by the operator precedence. From higher to lower precedence, the most common operators are:
- Multiplication (
*), division (/), remainder (%) - Add (
+), subtract (-) - Comparisons (
==,!=,<,>,<=,>=) - Logical AND (
&&) and OR (||) - Ternary conditional (
?:) - Assignment and compound assignment operators (
=,+=and so on)
This means that the above expression is resolved first calculating the multiplication, and then the sum:
let amount = 1 + 2 * 3 // = 7The full table of precedence, more complicated, is available at https://developer.apple.com/documentation/swift/swift_standard_library/operator_declarations.
When inside an expression you have multiple operators with the same precedence, we make use of the operator associativity. Associativity is a property we use to determine which operation has priority when the precedence is the same.
For example, consider this:
let amount = 4 / 2 * 5Depending on whether we first execute 4 / 2 or 2 * 5, the result could be 10 or 0.4.
Associativity solves this. Multiplication is left associative, so we must first execute the expression on the left. Parentheses let you specify the order explicitly:
let amount = (4 / 2) * 5Multiplication (*), division (/), remainder (%), add (+), subtract (-), logical AND (&&), logical OR (||) are left associative
Assignment and compound assignment operators (=, += and so on) and the ternary conditional (?:) are right associative
Comparisons (==, !=, <, >, <=, >=) don’t have associativity.