| /// Zero-Sized Type (ZST) for internal `BTreeSet` values. |
| /// Used instead of `()` to differentiate between: |
| /// * `BTreeMap<T, ()>` (possible user-defined map) |
| /// * `BTreeMap<T, SetValZST>` (internal set representation) |
| #[derive(Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Clone, Default)] |
| pub struct SetValZST; |
| |
| /// A trait to differentiate between `BTreeMap` and `BTreeSet` values. |
| /// Returns `true` only for type `SetValZST`, `false` for all other types (blanket implementation). |
| /// `TypeId` requires a `'static` lifetime, use of this trait avoids that restriction. |
| /// |
| /// [`TypeId`]: std::any::TypeId |
| pub trait IsSetVal { |
| fn is_set_val() -> bool; |
| } |
| |
| // Blanket implementation |
| impl<V> IsSetVal for V { |
| default fn is_set_val() -> bool { |
| false |
| } |
| } |
| |
| // Specialization |
| impl IsSetVal for SetValZST { |
| fn is_set_val() -> bool { |
| true |
| } |
| } |