Expression switches

In an expression switch, the switch expression is evaluated and the case expressions, which need not be constants, are evaluated left-to-right and top-to-bottom; the first one that equals the switch expression triggers execution of the statements of the associated case; the other cases are skipped. If no case matches and there is a “default” case, its statements are executed. There can be at most one default case and it may appear anywhere in the “switch” statement. A missing switch expression is equivalent to the boolean value true.

ExprSwitchStmt = "switch" [ SimpleStmt ";" ] [ Expression ] "{" { ExprCaseClause } "}" .
ExprCaseClause = ExprSwitchCase ":" StatementList .
ExprSwitchCase = "case" ExpressionList | "default" .

There’s a lot packed into that paragraph. But most of it is pretty intuitive, so doesn’t need a lot of special attention.

The main takeaways from this are:

• cases are evaluated top-to-bottom. This means that if you cases that aren’t completely exclusive of each other, the one listed first takes priority. For example:

  switch {
  	case x == 3:
  		/* x is exactly 3 */
  	case x > 0:
  		/* x is greater than 0, but not 3 */
  	default:
  		/* x is less than or equal to 0 */
  }
  

• the location of the default case doesn’t matter. This means the following code is equivalent to the previous example:

  switch {
  	default:
  		/* x is less than or equal to 0 */
  	case x == 3:
  		/* x is exactly 3 */
  	case x > 0:
  		/* x is greater than 0, but not 3 */
  }
  

  
  wever, I think it's good practice to put the `default` case at the end, just because it's easier to comprehend that way.
  

Quotes from The Go Programming Language Specification Language version go1.22 (Feb 6, 2024)