Persistent map
A persistent map is an immutable key-value collection whose updates produce new versions while preserving previous versions, typically through structural sharing.
C# Concurrency: Asynchronous and multithreaded programming
ImmutableDictionary<TKey,TValue> is a .NET generic dictionary whose contents cannot be changed after creation and whose modification methods return modified copies.
- How it is used
- Stores frequently changing shared data, such as e-commerce inventory, when immutable reads and coordinated replacements are useful.
- How deep it goes
- Explains read and copy-on-write APIs, builders, variable synchronization, and compare-and-retry updates, while deferring implementation internals.
- Examples
- Demonstrates book inventory purchases, SetItem-based copies, and an ImmutableInterlocked.TryUpdate retry loop.
- What you can do after
- Apply ImmutableDictionary APIs and diagnose unsafe shared-variable updates by switching compound modifications to ImmutableInterlocked.
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Fabulous Adventures in Data Structures and Algorithms
ImmutableDictionary is a .NET immutable key-value collection type that preserves prior versions when updated.
- How it is used
- Represents graph adjacency and can provide immutable arguments for memoized substitution operations.
- How deep it goes
- Describes a .NET map and its multivalue wrapper, including operations and stated O(1) costs, but not the collection's internals.
- Examples
- Uses node-to-neighbor mappings and a C# wrapper that associates keys with immutable sets of values.
- What you can do after
- Build a multivalue map by wrapping .NET's ImmutableDictionary with immutable sets and add, remove, and lookup operations.
Read how Fabulous Adventures in Data Structures and Algorithms explains persistent map →
Related concepts
- Mapkind of · A map is an associative data structure that stores key-value pairs and supports retrieving values by key.
- reconciliationused by · Reconciliation is the process of comparing related states, records, or outputs to identify differences and, when needed, resolve them or bring them into agreement.
- persistent data structurekind of · A persistent data structure preserves access to previous versions because updates create new versions without modifying existing ones.
- immutable collectionkind of · An immutable collection is a collection whose membership and contents cannot be changed after creation.
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