In C#, why Equals() method on arrays only compare their references, not their actual content

by

Although Microsoft’s Framework classes are unfortunately a bit inconsistent with regard to what Object.Equals(Object) means, in general X.Equals(Y) will only be true if replacing arbitrary references to X with references to Y, and/or vice versa, would not be expected to alter the semantics of the objects in question. For example, if X is a String with the content “Hello”, and Y is a different string with that same content, replacing references to one string with references to the other would not generally alter their behavior. Although code which uses ReferenceEquals to test whether two string references refer to the same string might notice the switch, normal string code would not.

As a general rule, no mutable object is equivalent to any other, and thus no reference to a mutable object should be equivalent to another unless both references refer to the same object. There is a big difference between having references to two different instances of int[], both of which hold the same values, versus having two references to the same instance. While it would be helpful for Array to have ItemsEqual methods which would test whether all items of the arrays, or certain ranges of items, matched, and it would be helpful to have an ImmutableArray type with a Equals/GetHashCode members that would regard as equal two immutable arrays with the same content, it is entirely right and proper that distinct mutable arrays compare unequal to each other regardless of content.

More Related Contents:

  1. Are arrays or lists passed by default by reference in c#?
  2. Two different “strings” are the same object instance?
  3. C# foreach loop take values from outer loop to inner loop
  4. How to put char ('X') to int array?
  5. Converting strings to arrays c#
  6. Merge two arrays and return sorted array in c# [closed]
  7. Pass an array of integers to ASP.NET Web API?
  8. Adding values to a C# array
  9. Byte array to image conversion
  10. What use is the Aliases property of assembly references in Visual Studio 8
  11. How to resize multidimensional (2D) array in C#?
  12. How to reference generic classes and methods in xml documentation
  13. How big is an object reference in .NET?
  14. Overhead of a .NET array?
  15. How to “flatten” or “index” 3D-array in 1D array?
  16. Store a reference to a value type?
  17. Testing equality of arrays in C#
  18. Copy Arrays to Array
  19. (.1f+.2f==.3f) != (.1f+.2f).Equals(.3f) Why?
  20. Correlation of two arrays in C#
  21. How to get a dimension (slice) from a multidimensional array
  22. Pick Random String From Array
  23. Random number generator in C# – unique values
  24. C# Permutation of an array of arraylists?
  25. Equality comparison between multiple variables
  26. Iterate through 2 dimensional array c#
  27. Why can’t I use the array initializer with an implicitly typed variable?
  28. Casting array to IEnumerable
  29. Making an array of random ints
  30. When to use ArrayList over array[] in c#?

Leave a Comment