System.Generics.Collections.TDictionary
Delphi
TDictionary<TKey,TValue> = class(TEnumerable<TPair<TKey,TValue>>)
C++
template<typename TKey, typename TValue> class PASCALIMPLEMENTATION TDictionary__2 : public TEnumerable__1<TPair__2<TKey,TValue> >
Properties
| Type | Visibility | Source | Unit | Parent |
|---|---|---|---|---|
| class | public | System.Generics.Collections.pas System.Generics.Collections.hpp |
System.Generics.Collections | System.Generics.Collections |
Description
Collection of key-value pairs.
TDictionary represents a generic collection of key-value pairs.
This class provides a mapping from a collection of keys to a collection of values. When you create a TDictionary object, you can specify such parameters as initial capacity, equality operation, and initial content.
You can add a key that is associated with a corresponding value with the Add or AddOrSetValue methods. You can remove entries with Remove or Clear (removes all key-value pairs). Adding or removing a key-value pair and looking up a key are efficient, close to O(1), because keys are hashed. A key must not be nil (though a value may be nil) and there must be an equality comparison operation for keys.
You can test presence of keys and values with the TryGetValue, ContainsKey, and ContainsValue methods.
The Items property lists all dictionary entries. You can also set and get values by indexing the Items property. Setting the value this way overwrites any existing value.
The class TObjectDictionary inherits from TDictionary and provides an automatic mechanism for freeing objects removed from dictionary entries.
Access methods
This section summarizes methods for reading and writing TDictionary or TObjectDictionary, including the effect of duplicate keys when writing, or key not found when reading.
Write
| Method | Index type | Value type | If duplicate key |
|---|---|---|---|
| Add | TKey | TValue | Exception |
| AddOrSetValue | TKey | TValue | Overwrite |
| Items | TKey | TValue | Overwrite |
Read
| Method | Index/input type | Result type | If key not found | Notes |
|---|---|---|---|---|
| ContainsKey | TKey | Boolean | false | True = found |
| ContainsValue | TValue | Boolean | n/a | True = found |
| ExtractPair | TKey | TPair | Default pair | Returns TPair, removes item from dictionary |
| Items | TKey | TValue | Exception | Use TryGetValue to avoid exception |
| operator [] | TKey | TValue | Exception | C++ only |
| Keys | n/a | TKeyCollection | n/a | |
| ToArray | n/a | TArray<TPair<TKey,TValue>> | n/a | |
| TryGetValue | TKey | TValue, Boolean | default, false | Returns TValue |
| Values | n/a | TValueCollection | n/a |
See Also
- Data.DBXCommon.TKey
- System.Rtti.TValue
- System.Generics.Collections.TDictionary.TKeyCollection
- System.Generics.Collections.TDictionary.TValueCollection
- System.Generics.Collections.TObjectDictionary
- System.Generics.Collections.TDictionary.Count
- System.Generics.Collections.TDictionary.Items
- System.Generics.Collections.TDictionary.Add
- System.Generics.Collections.TDictionary.AddOrSetValue
- System.Generics.Collections.TDictionary.Clear
- System.Generics.Collections.TDictionary.ContainsKey
- System.Generics.Collections.TDictionary.ContainsValue
- System.Generics.Collections.TDictionary.Remove
- System.Generics.Collections.TDictionary.TryGetValue