Dictionary<TKey,

Struct · namespace System

struct Dictionary<TKey, TValue> where TKey : IEquatable<TKey>, IHashable

A hash table (separate chaining). Keys keep their insertion order in Keys(), Values() and Entries() as long as no entry was removed.

using System;

var ages = Dictionary<string, int>.Create();
ages.Set("Ann", 31);
if (ages.TryGet("Ann") is int age)
    Console.WriteLine(age);
foreach (var key in ages.Keys())
    Console.WriteLine(key);

TKey must be IEquatable and IHashable: numbers, bool, char, enums and string are, and your own structs are as soon as they define ‘bool Equals(T other)’ and ‘int GetHashCode()’.

Like List<T>, a Dictionary is a handle to shared storage (see List), made by Dictionary<K, V>.Create(). The zero value (new(), a field without a value) is an empty dictionary that can be read but not changed: Set panics.

dict[key] reads a value (Dictionary<TKey, TValue>.Get), dict[key] = value sets one (Dictionary<TKey, TValue>.Set).

Static methods

Name	Description
Create	A new, empty dictionary.

Create

static Dictionary<TKey, TValue> Create()

A new, empty dictionary.

Methods

Name	Description
IsCreated	Whether the dictionary has storage: made by Create(), not the zero value (which cannot change).
Count	The number of entries.
ContainsKey	Whether the dictionary has an entry for key.
TryGet	The value of key, if there is one: if (ages.TryGet("Ann") is int age) ....
Get	The value of key (also dict[key]).
GetOrDefault	The value of key, or fallback if the key is not present.
Set	Adds an entry, or replaces the value of an existing key (also dict[key] = value).
Add	Adds an entry for a new key.
Remove	Removes the entry of key.
Clear	Removes all entries.
Keys	A new array with the keys, in insertion order as long as no entry was removed.
Values	A new array with the values, in the order of Dictionary<TKey, TValue>.Keys.
Entries	A new array with the entries (key and value), in the order of Dictionary<TKey, TValue>.Keys: foreach (var e in ages.Entries()) Console.WriteLine(e.Key + " " + e.Value.ToString());.

IsCreated

bool IsCreated()

Whether the dictionary has storage: made by Create(), not the zero value (which cannot change).

Since 0.26

Count

int Count()

The number of entries.

ContainsKey

bool ContainsKey(TKey key)

Whether the dictionary has an entry for key.

TryGet

Optional<TValue> TryGet(TKey key)

The value of key, if there is one: if (ages.TryGet("Ann") is int age) ....

Returns nothing (null) if the key is not present.

Get

TValue Get(TKey key)

The value of key (also dict[key]). Dictionary<TKey, TValue>.TryGet asks without panicking.

Panics when the key is not present.

Since 0.04

GetOrDefault

TValue GetOrDefault(TKey key, TValue fallback)

The value of key, or fallback if the key is not present.

Set

void Set(TKey key, TValue value)

Adds an entry, or replaces the value of an existing key (also dict[key] = value).

Panics when the dictionary was not created (Dictionary<TKey, TValue>.IsCreated).

Add

Error<void> Add(TKey key, TValue value)

Adds an entry for a new key.

Returns an error if the key exists already (the dictionary is not changed).

Remove

bool Remove(TKey key)

Removes the entry of key.

Returns whether there was an entry.

Clear

void Clear()

Removes all entries.

Keys

TKey[] Keys()

A new array with the keys, in insertion order as long as no entry was removed.

Values

TValue[] Values()

A new array with the values, in the order of Dictionary<TKey, TValue>.Keys.

Entries

KeyValuePair<TKey, TValue>[] Entries()

A new array with the entries (key and value), in the order of Dictionary<TKey, TValue>.Keys: foreach (var e in ages.Entries()) Console.WriteLine(e.Key + " " + e.Value.ToString());.