Switch Expressions in

About Switch Expressions

Switch expressions behave in a similar manner to switch statements covered in switch-statements. They support a kind of decision table that maps input conditions to actions or values.

At the core of the switch expression is pattern matching. In the coding exercise we matched values against const patterns. In this case the inputs to the switch are a range expression which is matched to const values and the values used by the case guards.

The cases (also known as switch arms) are evaluated in text order and the process is cut short and the associated value is returned as soon as a match is found.

The _ case which is the last in the list is useful to ensure that the matching is exhaustive and to avoid possible run-time errors.

double xx = 42d;

string interesting = xx switch
{
    0 => "I suppose zero is interesting",
    3.14 when DateTime.Now.Day == 14 && DateTime.Now.Month == 3 => "Mmm pie!",
    3.14 => "π",
    42 => "a bit of a cliché",
    1729 => "only if you are a pure mathematician",
    _ => "not interesting"
};

// => interesting == "a bit of a cliché"

An "arm" of the switch is selected when the pattern matches the range variable and any case guard evaluates to true.

Switch expression also support type patterns and recursive matching.