Switch

A switch statement allows the selective execution of one of several blocks of code based on the value of an expression. It can be thought of as an expanded if ... else statement, with many potential if clauses.

Syntax 1

There are many syntaxes that can be used in the switch statement. The following is probably the most common:

switch <expression> {
case <value 1>:
  <statements>
case <value 2>:
  <statements>
.
.
.
case <value N>:
  <statements>
default:
  <statements>
}

When <expression> is equal to the value of one of the case statements, the corresponding <statements> block is executed. If the <expression> matches none of the case values, then the optional default statements block is executed. If the default block is omitted, and none of the values are matched, none of the statements in the switch block are executed.

In Go, the switch statement differs from other languages like C++ and Java in that the values used by the case statements are not limited to constants. They can also be variables or full expressions. Additionally, Go only executes the selected case <expressions> block, or the default block, so no “break” statement is needed. Code execution automatically resumes after the switch statement.

Syntax 2

The <expression> after the switch can be omitted, making the cases behave more like expressions in if... else statements:

switch {
case <expression 1>:
  <statements>
case <expression 2>:
  <statements>
    .
    .
    .
case <expression N>
  <statements>
default:
  <statements>
}

The first case <expression> that evaluates to true will execute its corresponding <statements>. Again, the default block is optional, and will execute its <statements> if none of the case statements are executed.

This is equivalent to:

switch true { ... }

Syntax 3

In each case, a given case statement can have more than one matching value (or expression), separated by commas:

switch <expression> {
case <value 1>, <value 2>, ... <value N>:
  <statements>
    .
    .
    .
default:
  <statements>
}

Values are compared left-to-right and top-to-bottom. The first case block to match the switch expression will be executed.

Example

In the example below, a variable i is declared and used in a switch expression to test whether the result will be even or odd:

i := 7
switch i % 2 {
case 0:
   fmt.Printf("%d is even.\n",i)
case 1:
   fmt.Printf("%d is odd.\n",i)
}

// Output: 7 is odd.

Codebyte Example

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