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Introduction

Switch statements provide a clean way to express conditionals across many branches. Go’s switch is more powerful than in many other languages, supporting multiple expressions per case, automatic break behavior, and even type switches.

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The Code

// _Switch statements_ express conditionals across many
// branches.

package main

import (
	"fmt"
	"time"
)

func main() {

	// Here's a basic `switch`.
	i := 2
	fmt.Print("Write ", i, " as ")
	switch i {
	case 1:
		fmt.Println("one")
	case 2:
		fmt.Println("two")
	case 3:
		fmt.Println("three")
	}

	// You can use commas to separate multiple expressions
	// in the same `case` statement. We use the optional
	// `default` case in this example as well.
	switch time.Now().Weekday() {
	case time.Saturday, time.Sunday:
		fmt.Println("It's the weekend")
	default:
		fmt.Println("It's a weekday")
	}

	// `switch` without an expression is an alternate way
	// to express if/else logic. Here we also show how the
	// `case` expressions can be non-constants.
	t := time.Now()
	switch {
	case t.Hour() < 12:
		fmt.Println("It's before noon")
	default:
		fmt.Println("It's after noon")
	}

	// A type `switch` compares types instead of values.  You
	// can use this to discover the type of an interface
	// value.  In this example, the variable `t` will have the
	// type corresponding to its clause.
	whatAmI := func(i interface{}) {
		switch t := i.(type) {
		case bool:
			fmt.Println("I'm a bool")
		case int:
			fmt.Println("I'm an int")
		default:
			fmt.Printf("Don't know type %T\n", t)
		}
	}
	whatAmI(true)
	whatAmI(1)
	whatAmI("hey")
}

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Switch Variants

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Basic Switch

i := 2
switch i {
case 1:
	fmt.Println("one")
case 2:
	fmt.Println("two")
case 3:
	fmt.Println("three")
}
The standard switch compares a value against multiple cases. Unlike C or Java, Go automatically breaks after each case - no break statement needed!
Go’s switch cases break automatically. You don’t need (and shouldn’t use) explicit break statements unless you want to exit early from within a case.

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Multiple Expressions in Case

switch time.Now().Weekday() {
case time.Saturday, time.Sunday:
	fmt.Println("It's the weekend")
default:
	fmt.Println("It's a weekday")
}
Use commas to test multiple values in a single case. The default case runs when no other cases match.

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Expression-less Switch (If/Else Alternative)

t := time.Now()
switch {
case t.Hour() < 12:
	fmt.Println("It's before noon")
default:
	fmt.Println("It's after noon")
}
A switch without an expression is equivalent to switch true. This provides a cleaner way to write long if-else chains.
Use expression-less switch when you have multiple unrelated conditions to check. It’s more readable than multiple if/else if statements.

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Type Switch

whatAmI := func(i interface{}) {
	switch t := i.(type) {
	case bool:
		fmt.Println("I'm a bool")
	case int:
		fmt.Println("I'm an int")
	default:
		fmt.Printf("Don't know type %T\n", t)
	}
}
whatAmI(true)   // I'm a bool
whatAmI(1)      // I'm an int
whatAmI("hey")  // Don't know type string
Type switches compare types instead of values. This is useful when working with interfaces to determine the underlying type.
In a type switch, the variable t has a different type in each case block, matching the type specified in that case.

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Switch Features

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Automatic Break

Unlike C/Java, Go switches break automatically - no fall-through by default.

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Non-Constant Cases

Cases can be expressions, not just constants: 
switch {
case x > 10:
    // ...
case y < 5:
    // ...
}

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Default Case

The default case is optional and can appear anywhere (though by convention it’s usually last): 
switch x {
default:
    fmt.Println("default")
case 1:
    fmt.Println("one")
}

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Common Patterns

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Value Matching

switch status {
case "active":
    // handle active
case "pending":
    // handle pending
case "inactive":
    // handle inactive
}

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Range Checking

switch {
case age < 18:
    category = "minor"
case age < 65:
    category = "adult"
default:
    category = "senior"
}

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Type Detection

switch v := x.(type) {
case string:
    fmt.Printf("string: %s\n", v)
case int:
    fmt.Printf("int: %d\n", v)
}

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Switch vs If/Else

Use Switch WhenUse If/Else When
Multiple values for one variableDifferent variables in conditions
Checking type of interfaceComplex boolean logic
Many branches (3+)Simple binary decision

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Key Takeaways

  • Switch cases break automatically - no explicit break needed
  • Multiple values can be tested in one case using commas
  • Expression-less switch (switch { }) is great for if/else chains
  • Type switches determine the type of interface values
  • Cases can be expressions, not just constants
  • The default case is optional and handles unmatched cases
  • Go’s switch is more powerful and flexible than in C/Java

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