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Document alt record patterns

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Brian Anderson 2011-10-28 16:51:11 -07:00
parent 6afecc37e3
commit 6864070b24
1 changed files with 35 additions and 6 deletions
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doc/rust.texi
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@ -3369,12 +3369,12 @@ expression following the @code{alt} when the case block completes.
@cindex Pattern alt expression
@cindex Control-flow
A pattern @code{alt} expression branches on a @emph{pattern}. The exact form of
matching that occurs depends on the pattern. Patterns consist of some
combination of literals, tag constructors, variable binding specifications and
placeholders (@code{_}). A pattern @code{alt} has a @emph{head expression},
which is the value to compare to the patterns. The type of the patterns must
equal the type of the head expression.
A pattern @code{alt} expression branches on a @emph{pattern}. The exact form
of matching that occurs depends on the pattern. Patterns consist of some
combination of literals, destructured tag constructors, records and tuples,
variable binding specifications and placeholders (@code{_}). A pattern
@code{alt} has a @emph{head expression}, which is the value to compare to the
patterns. The type of the patterns must equal the type of the head expression.
To execute a pattern @code{alt} expression, first the head expression is
evaluated, then its value is sequentially compared to the patterns in the arms
@ -3411,6 +3411,35 @@ variant @code{nil} from a binding to variable @code{nil}. Without the period
the value of @code{x} would be bound to variable @code{nil} and the compiler
would issue an error about the final wildcard case being unreachable.
Records can also be pattern-matched and their fields bound to variables.
When matching fields of a record, the fields being matched are specified
first, then a placeholder (@code{_}) represents the remaining fields.
@example
fn main() @{
let r = @{
player: "ralph",
stats: load_stats(),
options: @{
choose: true,
size: "small"
@}
@};
alt r @{
@{options: @{choose: true, _@}, _@} @{
choose_player(r)
@}
@{player: p, options: @{size: "small", _@}, _@} @{
log p + " is small";
@}
_ @{
next_player();
@}
@}
@}
@end example
Multiple alternative patterns may be joined with the @code{|} operator. A
range of values may be specified with @code{to}. For example: