I read these docs about structs, but I don't understand about unit structs. It says:
Unit structs are most commonly used as marker. They have a size of zero bytes, but unlike empty enums they can be instantiated, making them isomorphic to the unit type
(). Unit structs are useful when you need to implement a trait on something, but don’t need to store any data inside it.
they only give this piece of code as an example:
struct Unit;
What is a real world example of using a unit struct?
GlobalThe global memory allocator, Global, is a unit struct:
pub struct Global;
It has no state of its own (because the state is global), but it implements traits like Allocator.
std::fmt::ErrorThe error for string formatting, std::fmt::Error, is a unit struct:
pub struct Error;
It has no state of its own, but it implements traits like Error.
RangeFullThe type for the .. operator, RangeFull, is a unit struct:
pub struct RangeFull;
It has no state of its own, but it implements traits like RangeBounds.
chrono::UtcThe Utc timezone is a unit struct:
pub struct Utc;
It has no state of its own, but it implements traits like TimeZone and is thus usable as a generic argument to Date and DateTime.