Switch

When you're choosing between more than two or three branches, an if/else if ladder gets noisy. Go's switch is built for exactly that job — and it fixes the sharpest edge the C-family version has.

Cases break by default

In C, every case falls through into the next one unless you remember to write break — forget it once and two branches quietly run. Decades of bugs came from that default. Go flips it: each case breaks automatically.

package main

import "fmt"

func main() {
	day := "saturday"
	switch day {
	case "saturday":
		fmt.Println("weekend!")
	case "sunday":
		fmt.Println("still weekend!")
	default:
		fmt.Println("back to work")
	}
}

Only the matching case runs — no break needed, no accidental fall-through possible. (A fallthrough keyword exists for the rare day you truly want the C behavior, but you must ask for it explicitly, which is the point: the dangerous thing is now the verbose thing.)

Notice default: it runs when nothing else matches, and it doesn't have to come last — though it usually does.

Several values, one case

When multiple values share a branch, list them in one case, separated by commas — this is Go's answer to C's stacked empty cases:

package main

import "fmt"

func main() {
	day := "sunday"
	switch day {
	case "saturday", "sunday":
		fmt.Println("weekend!")
	default:
		fmt.Println("back to work")
	}
}

Switch with no condition

Drop the value after switch entirely and each case becomes a boolean expression — the first true one wins. It reads like an if/else if chain, but flatter:

package main

import "fmt"

func main() {
	score := 74
	switch {
	case score >= 90:
		fmt.Println("excellent")
	case score >= 50:
		fmt.Println("pass")
	default:
		fmt.Println("try again")
	}
}

This is idiomatic Go whenever a chain grows past two or three branches: the conditions line up vertically and every outcome is easy to scan. Like if and for, a switch can also take an init statement: switch x := compute(); { ... }.

One sentence on type switches

There's a second kind of switch — switch v := x.(type) — that branches on what type a value has rather than what value it holds; it belongs to the interfaces chapter, so file it away for later.

Time to put switch to work: the exercise maps HTTP status codes to their standard reason phrases — a real function that real servers need, and a perfect shape for one switch statement.