= The switch Statement

.Syntax
[source,unlang]
----
switch <expansion> {
    case <match-1> {
        [ statements-1 ]
    }
    case <match-2> {
        [ statements-2 ]
    }
    case {
        [ statements-3 ]
    }
}
----

A `switch` statement causes the server to evaluate _expansion_, which
can be an xref:attr.adoc[&Attribute-Name] or
xref:condition/operands.adoc[data].  The result is compared against _match-1_
and _match-2_ to find a match. If no string matches, then the server
looks for the default xref:case.adoc[case] statement, which has no
associated match.

The matching is done via equality.  The `switch` statement is mostly
syntactic sugar and is used to simplify the visual form of the
configuration.  It is mostly equivalent to the following use of
xref:if.adoc[if] statements:

.Nearly equivalent syntax
[source,unlang]
----
if (<expansion> == <match-1>) {
    [ statements-1 ]
}
elsif (<expansion> == <match-2>) {
    [ statements-2 ]
}
else {
    [ statements-3 ]
}
----

The only difference between the two forms is that for a `switch`
statement, the _expansion_ is evaluated only once.  For the equivalent
xref:if.adoc[if] statement, the _expansion_ is evaluated again for every
xref:if.adoc[if].

If a matching xref:case.adoc[case] is found, the statements within
that xref:case.adoc[case] are evaluated. If no matching
xref:case.adoc[case] is found, the `case` section with no "match" is
evaluated. If there is no such `case { ...}` subsection, then the
`switch` statement behaves as if the `case {...}` section was empty.

////
For compatibility with version 3, and empty `case` statement can also
be used instead of `default`.
////

The _match_ text for the xref:case.adoc[case] statement can be an
xref:attr.adoc[&Attribute-Name] or xref:type/index.adoc[data].

No statement other than xref:case.adoc[case] can appear in a `switch`
statement, and the xref:case.adoc[case] statement cannot appear outside of a
`switch` statement.

.Example
[source,unlang]
----
switch &User-Name {
    case "bob" {
        reject
    }

    case {
        ok
    }
}
----

// Copyright (C) 2020 Network RADIUS SAS.  Licenced under CC-by-NC 4.0.
// Development of this documentation was sponsored by Network RADIUS SAS.