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marker type

An empty type used only as a label inside another type, like Km in Distance.

A unit struct never created at run time, used as a type argument (often with PhantomData) to select impls or keep values apart.

Examples

  • With struct Parcel; and struct Courier; as markers, passing an Id<Courier> where an Id<Parcel> is expected fails with E0308.

See also

PhantomData typestate newtype
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