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Dictionary<TKey, TValue> Constructor (IEqualityComparer<TKey>)

Initializes a new instance of the Dictionary<TKey, TValue> class that is empty, has the default initial capacity, and uses the specified IEqualityComparer<T>.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

public:
Dictionary(
	IEqualityComparer<TKey>^ comparer
)

Parameters

comparer
Type: System.Collections.Generic::IEqualityComparer<TKey>

The IEqualityComparer<T> implementation to use when comparing keys, or nullptr to use the default EqualityComparer<T> for the type of the key.

Use this constructor with the case-insensitive string comparers provided by the StringComparer class to create dictionaries with case-insensitive string keys.

Every key in a Dictionary<TKey, TValue> must be unique according to the specified comparer.

Dictionary<TKey, TValue> requires an equality implementation to determine whether keys are equal. If comparer is nullptr, this constructor uses the default generic equality comparer, EqualityComparer<T>::Default. If type TKey implements the System::IEquatable<T> generic interface, the default equality comparer uses that implementation.

NoteNote

If you can estimate the size of the collection, using a constructor that specifies the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Dictionary<TKey, TValue>.

This constructor is an O(1) operation.

The following code example creates a Dictionary<TKey, TValue> with a case-insensitive equality comparer for the current culture. The example adds four elements, some with lower-case keys and some with upper-case keys. The example then attempts to add an element with a key that differs from an existing key only by case, catches the resulting exception, and displays an error message. Finally, the example displays the elements in the dictionary.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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