Enum DefaultComparator

pub enum DefaultComparator {}

A representation of LMDB’s default comparator behavior.

This enum is used to indicate the absence of a custom comparator for an LMDB database instance. When a Database is created or opened with DefaultComparator, it signifies that the comparator should not be explicitly set via ffi::mdb_set_compare. Consequently, the database instance utilizes LMDB’s built-in default comparator, which inherently performs lexicographic comparison of keys.

This comparator’s lexicographic implementation is employed in scenarios involving prefix iterators. Specifically, methods other than Comparator::compare are utilized to determine the lexicographic successors and predecessors of byte sequences, which is essential for these iterators’ operation.

When a custom comparator is provided, the wrapper is responsible for setting it with the ffi::mdb_set_compare function, which overrides the default comparison behavior of LMDB with the user-defined logic.

Trait Implementations

impl LexicographicComparator for DefaultComparator

fn compare_elem(a: u8, b: u8) -> Ordering

Compare a single byte; this function is used to implement Comparator::compare by definition of lexicographic ordering.

fn successor(elem: u8) -> Option<u8>

Advances the given elem to its immediate lexicographic successor, if possible. Returns None if elem is already at its maximum value with respect to the lexicographic order defined by this comparator.

fn predecessor(elem: u8) -> Option<u8>

Moves the given elem to its immediate lexicographic predecessor, if possible. Returns None if elem is already at its minimum value with respect to the lexicographic order defined by this comparator.

fn max_elem() -> u8

Returns the maximum byte value per the comparator’s lexicographic order.

fn min_elem() -> u8

Returns the minimum byte value per the comparator’s lexicographic order.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 0 bytes (uninhabited)