Conditions

Control program flow in Go using if-else statements and switch cases with pattern matching

If-else Statement

Executes a block of code when a condition is true.

if condition {
    // code runs if condition is true
} else if anotherCondition {
    // code runs if it gets here and anotherCondition is true
} else {
    // code runs if none of the above are true
}

Scoped Variables

Go lets you declare a variable that only exists in the if and else blocks:

s := "Hello"

if n := len(s); n == 1 {
	fmt.Println("Length is", n)
} else if n >= 2 {
	fmt.Println("Length is", n)
} else {
	fmt.Println("Empty string")
}

// Length is 5

fmt.Println("Length is", n) // undefined: n (compiler)

Switch Statement

Executes the matching case block.

switch expression {
case value1:
    // code runs if expression == value1
case value2:
    // code runs if expression == value2
case value3, value4:
    // code runs if expression == value3 or value4
default:
    // code runs if expression does not match any case
}

Go auto break after each case implicitly, but the keyword can still be used.

Fallthrough Behavior

Since Go breaks after each case by default, the fallthrough keyword allows you to explicitly override this behavior when sequential processing is needed.

a := 2

switch a {
case 1:
    fmt.Println("One")
case 2:
    fmt.Println("Two")
    fallthrough
case 3:
    fmt.Println("Three")
case 4:
    fmt.Println("Four")
default:
    fmt.Println("None of above")
}

// Two
// Three

Expression-less Switch

Omitting the expression makes the switch statement act like an if-else statement:

a := 3

switch {
case a == 1:
    fmt.Println("One")
case a == 2:
    fmt.Println("Two")
case a == 3 || a == 4:
    fmt.Println("Three or Four")
default:
    fmt.Println("None of above")
}

// Three or Four