Comparer<'T> Class

 

Provides a base class for implementations of the IComparer<'T> generic interface.

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

System.Object
  System.Collections.Generic.Comparer<'T>

[<AbstractClass>]
[<SerializableAttribute>]
type Comparer<'T> = 
    class
        interface IComparer
        interface IComparer<'T>
    end

Type Parameters

T

The type of objects to compare.

NameDescription
System_CAPS_protmethodComparer<'T>()

Initializes a new instance of the Comparer<'T> class.

NameDescription
System_CAPS_pubpropertySystem_CAPS_staticDefault

Returns a default sort order comparer for the type specified by the generic argument.

NameDescription
System_CAPS_pubmethodCompare('T, 'T)

When overridden in a derived class, performs a comparison of two objects of the same type and returns a value indicating whether one object is less than, equal to, or greater than the other.

System_CAPS_pubmethodSystem_CAPS_staticCreate(Comparison<'T>)

Creates a comparer by using the specified comparison.

System_CAPS_pubmethodEquals(Object)

Determines whether the specified object is equal to the current object.(Inherited from Object.)

System_CAPS_protmethodFinalize()

Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)

System_CAPS_pubmethodGetHashCode()

Serves as the default hash function. (Inherited from Object.)

System_CAPS_pubmethodGetType()

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_protmethodMemberwiseClone()

Creates a shallow copy of the current Object.(Inherited from Object.)

System_CAPS_pubmethodToString()

Returns a string that represents the current object.(Inherited from Object.)

NameDescription
System_CAPS_pubinterfaceSystem_CAPS_privmethodIComparer.Compare(Object, Object)

Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other.

Derive from this class to provide a custom implementation of the IComparer<'T> interface for use with collection classes such as the SortedList<'TKey, 'TValue> and SortedDictionary<'TKey, 'TValue> generic classes.

The difference between deriving from the Comparer<'T> class and implementing the System.IComparable interface is as follows:

  • To specify how two objects should be compared by default, implement the System.IComparable interface in your class. This ensures that sort operations will use the default comparison code that you provided.

  • To define a comparer to use instead of the default comparer, derive from the Comparer<'T> class. You can then use this comparer in sort operations that take a comparer as a parameter.

The object returned by the Default property uses the System.IComparable<'T> generic interface (IComparable<T> in C#, IComparable(Of T) in Visual Basic) to compare two objects. If type T does not implement the System.IComparable<'T> generic interface, the Default property returns a Comparer<'T> that uses the System.IComparable interface.

Notes to Implementers:

Compare and EqualityComparer<'T>.Equals may behave differently in terms of culture-sensitivity and case-sensitivity.

For string comparisons, the StringComparer class is recommended over Comparer<String>. Properties of the StringComparer class return predefined instances that perform string comparisons with different combinations of culture-sensitivity and case-sensitivity. The case-sensitivity and culture-sensitivity are consistent among the members of the same StringComparer instance.

For more information on culture-specific comparisons, see the System.Globalization namespace and Globalizing and Localizing .NET Framework Applications.

The following example derives a class, BoxLengthFirst, from the Comparer<'T> class. This comparer compares two objects of type Box. It sorts them first by length, then by height, and then by width. The Box class implements the IComparable<'T> interface to control the default comparison between two Box objects. This default implementation sorts first by height, then by length, and then by width. The example shows the differences between the two comparisons by sorting a list of Box objects first by using the BoxLengthFirst comparer and then by using the default comparer.

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

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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