What Does Mutator Mean?

A mutator, in the context of C#, is a method, with a public level of accessibility, used to modify and control the value of a private member variable of a class. The mutator is used to assign a new value to the private field of a type. It forms a tool to implement encapsulation by only controlling access to the internal field values that must be modified.


The benefits of using a mutator include:

  • Prevents the user from directly accessing the private data of an object instance and allows access only through public methods to prevent data corruption.
  • Provides flexibility in modifying the internal representation of the fields of an object that represents the internal state without breaking the interface used by the object’s clients.
  • Ability to include additional processing logic like validation of a values set, triggering of events, etc., during the modification of the field in the mutator.
  • Provides the synchronization that is necessary for multithreading scenarios.
  • Includes a provision to override the mutator declared in a base class with the code in the derived class.

Techopedia Explains Mutator

A mutator is usually provided with an accessor that returns the value of the member variable. For data members that are immutable, the mutator should not be provided.

For example, StudentData can be a class that stores a student’s details, such as name, address, grade, etc. There can be a public method, SetGrade in the class. StudentData is the mutator to update the StudentData object from the code that uses the object.

While a mutator is implemented in C++ by an explicit public method to modify a private field, C# introduces “properties” as a new feature that implements a mutator to modify field values as well as an accessor to fetch the field. Each property is represented in the common intermediate language code with a pair of methods prefixed with “get_”(accessor) and “set_”(mutator) under the hood. They are called internally by the common language runtime (CLR). This simplifies the code and sometimes allows for the performance of mathematical operations.

The mutator is not often used in objects, where the object’s behavior is considered rather than how it performs.


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Margaret Rouse

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.