The case statement is similar to the if statement, but it represents a multi-branch selection. The expression after the keyword case is evaluated and if its value is in a slicelist the corresponding statements (after the of keyword) are executed. If the value is not in any given slicelist the else part is executed. If there is no else part and not all possible values that expr can hold occur in a slicelist, a static error occurs. This holds only for expressions of ordinal types. “All possible values” of expr are determined by expr’s type. To suppress the static error an else part with an empty discard statement should be used.

Because case statements are checked for exhaustiveness during semantic analysis, the value in every of branch must be a constant expression. This restriction also allows the compiler to generate more performant code.

The case statement doesn’t produce an l-value, so the following example won’t work: