mono/netcore/System.Private.CoreLib/shared/System/IComparable.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Diagnostics.CodeAnalysis;

namespace System
{
    // The IComparable interface is implemented by classes that support an
    // ordering of instances of the class. The ordering represented by
    // IComparable can be used to sort arrays and collections of objects
    // that implement the interface.
    // 
    public interface IComparable
    {
        // Interface does not need to be marked with the serializable attribute
        // Compares this object to another object, returning an integer that
        // indicates the relationship. An implementation of this method must return
        // a value less than zero if this is less than object, zero
        // if this is equal to object, or a value greater than zero
        // if this is greater than object.
        // 
        int CompareTo(object? obj);
    }

    // Generic version of IComparable.

    public interface IComparable<in T>
    {
        // Interface does not need to be marked with the serializable attribute
        // Compares this object to another object, returning an integer that
        // indicates the relationship. An implementation of this method must return
        // a value less than zero if this is less than object, zero
        // if this is equal to object, or a value greater than zero
        // if this is greater than object.
        // 
        int CompareTo([AllowNull] T other);
    }
}