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| -rw-r--r-- | doc/rust.md | 38 |
1 files changed, 37 insertions, 1 deletions
diff --git a/doc/rust.md b/doc/rust.md index d93670a5638..6ae38b07db2 100644 --- a/doc/rust.md +++ b/doc/rust.md @@ -761,7 +761,9 @@ fn main() { ##### Export declarations ~~~~~~~~ {.ebnf .gram} -export_decl : "export" ident [ ',' ident ] * ; +export_decl : "export" ident [ ',' ident ] * + | "export" ident "::{}" + | "export" ident '{' ident [ ',' ident ] * '}' ; ~~~~~~~~ An _export declaration_ restricts the set of local names within a module that @@ -813,6 +815,40 @@ mod foo { } ~~~~~~~~ +When exporting the name of an `enum` type `t`, by default, the module also +implicitly exports all of `t`'s constructors. For example: + +~~~~~~~~ +mod foo { + export t; + + enum t {a, b, c}; +} +~~~~~~~~ + +Here, `foo` imports `t`, `a`, `b`, and `c`. + +The second and third forms of export declaration can be used to export +an `enum` item without exporting all of its constructors. These two +forms can only be used to export an `enum` item. The second form +exports the `enum` type name without exporting any of its +constructors, achieving a simple kind of data abstraction. The third +form exports an `enum` type name along with a subset of its +constructors. For example: + +~~~~~~~~ +mod foo { + export abstract{}; + export slightly_abstract{a, b}; + + enum abstract {x, y, z} + enum slightly_abstract {a, b, c, d} +} +~~~~~~~~ + +Module `foo` exports the types `abstract` and `slightly_abstract`, as well as +constructors `a` and `b`, but doesn't export constructors `x`, `y`, `z`, `c`, +or `d`. ### Functions |