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| -rw-r--r-- | src/doc/trpl/structs.md | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/src/doc/trpl/structs.md b/src/doc/trpl/structs.md index 2f8d2bfdea0..ad7ead93199 100644 --- a/src/doc/trpl/structs.md +++ b/src/doc/trpl/structs.md @@ -177,3 +177,22 @@ println!("length is {} inches", integer_length); As you can see here, you can extract the inner integer type through a destructuring `let`, just as with regular tuples. In this case, the `let Inches(integer_length)` assigns `10` to `integer_length`. + +# Unit-like structs + +You can define a struct with no members at all: + +```rust +struct Electron; +``` + +Such a struct is called ‘unit-like’ because it resembles the empty +tuple, `()`, sometimes called ‘unit’. Like a tuple struct, it defines a +new type. + +This is rarely useful on its own (although sometimes it can serve as a +marker type), but in combination with other features, it can become +useful. For instance, a library may ask you to create a structure that +implements a certain [trait][trait] to handle events. If you don’t have +any data you need to store in the structure, you can just create a +unit-like struct. |