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IComparable(T) Interface

Defines a generalized comparison method that a value type or class implements to create a type-specific comparison method for ordering or sorting its instances.

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

type IComparable<'T> =  interface end

Type Parameters

in T

The type of object to compare.

This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.

The IComparable(T) type exposes the following members.

Public methodSupported by the XNA FrameworkSupported by Portable Class LibraryCompareToCompares the current instance with another object of the same type and returns an integer that indicates whether the current instance precedes, follows, or occurs in the same position in the sort order as the other object.

This interface is implemented by types whose values can be ordered or sorted and provides a strongly typed comparison method for ordering members of a generic collection object. For example, one number can be larger than a second number, and one string can appear in alphabetical order before another. It requires that implementing types define a single method, CompareTo(T), that indicates whether the position of the current instance in the sort order is before, after, or the same as a second object of the same type. Typically, the method is not called directly from developer code. Instead, it is called automatically by methods such as List(T).Sort() and Add.

Typically, types that provide an IComparable(T) implementation also implement the IEquatable(T) interface. The IEquatable(T) interface defines the Equals method, which determines the equality of instances of the implementing type.

The implementation of the CompareTo(T) method must return an Int32 that has one of three values, as shown in the following table.



Less than zero

This object precedes the object specified by the CompareTo method in the sort order.


This current instance occurs in the same position in the sort order as the object specified by the CompareTo method argument.

Greater than zero

This current instance follows the object specified by the CompareTo method argument in the sort order.

All numeric types (such as Int32 and Double) implement IComparable(T), as do String, Char, and DateTime. Custom types should also provide their own implementation of IComparable(T) to enable object instances to be ordered or sorted.

Notes to Implementers

Replace the type parameter of the IComparable(T) interface with the type that is implementing this interface.

If you implement IComparable(T), you should overload the op_GreaterThan, op_GreaterThanOrEqual, op_LessThan, and op_LessThanOrEqual operators to return values that are consistent with CompareTo. In addition, you should also implement IEquatable(T). See the IEquatable(T) article for complete information.

The following code example illustrates the implementation of IComparable(T) for a simple Temperature object. The example creates a SortedList(TKey, TValue) collection of strings with Temperature object keys, and adds several pairs of temperatures and strings to the list out of sequence. In the call to the Add method, the SortedList(TKey, TValue) collection uses the IComparable(T) implementation to sort the list entries, which are then displayed in order of increasing temperature.

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

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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