Generating Equality Members
Alt+Insert | Equality Members
The implementation of equality methods (i.e.
GetHashCode()) as well as equality operators (i.e.
!=) in the Object class guarantees reference equality. In a type you create (which ultimately derives from
Object and thus implements reference equality by default), you may want to implement value equality for objects of this type and use the hashcode as a unique object identifier for hashing purposes. In this case, you need to override equality methods and operators for your type.
ReSharper allows you to automate these routines with the Generate equality members command.
In the example below, this command is used to generate
GetHashCode() methods based on
|Before generation||After generation|
| || |
To generate overrides for equality members
In the Generate dialog that appears, select fields to be compared in the
Equals()method and to be included into the value generation in the
If there are no fields/properties in your type or you do not select any of them, ReSharper, depending on your settings, throws new
NotImplementedException(), returns default value, or puts code that will not compile in the body of the generated methods. You can configure the settings on the page of ReSharper options.
Optionally, use the following controls in the dialog:
- Fields can be null — appears if there are any nullable fields or properties in your type. By default, this check box is selected, meaning that ReSharper will generate null checks for selected fields. You can clear this check box if you do not need null checks.
- String comparison — appears if there are any string fields in your type. ReSharper will generate
string.Compare(string, string, StringComparison)for the selected strings, and the selector lets you choose which value should be generated for the StringComparison argument.
- GetHashCode already exists and Equals already exists appear if the corresponding overrides already exist and let you choose whether to:
- Replace the method if it already exists.
- Put the newly generated method side by side with the existing one.
- Skip generating a new method altogether.
- Overload equality operators — generates custom equality and inequality operators (i.e.
!=) for the current type.
- Implement IEquatable<T> interface implements a type-specific
- Comparand type check — allows you to choose how the
Equals()method will compare object types:
- Type exactly same as this
- Type exactly as the owner type
- Type is of the owner type or a subtype
You can also generate the two overrides by choosing Overriding Members in the Generate menu, but in that case they will both return base methods.
As an alternative to generating equality members within your type, you can generate equality comparer class for your type.
This feature is supported in the following languages and technologies:
The instructions and examples given here address the use of the feature in C#. For details specific to other languages, see corresponding topics in the ReSharper by Language section.
- MSDN: Equals() Method
- MSDN: GetHashCode() Method
- MSDN: Guidelines for Overriding Equals() and Operator == (C# Programming Guide)
- StackOverflow: Why is it important to override GetHashCode when Equals method is overridden?
- StackOverflow: What is the best algorithm for an overridden System.Object.GetHashCode?
- Equals() and GetHashCode() investigated by Kenneth Thorman