Mutator

A mutator is a term used across several fields to denote an agent, mechanism, or method that introduces changes to another system. Although the word shares a common root with mutation, its specific meaning varies by domain, including genetics, mutation testing in software engineering, and mutability in programming.

In genetics, a mutator allele or mutator gene increases the baseline mutation rate, usually by compromising DNA repair pathways or replication fidelity. Mutator phenotypes can accelerate evolution in microbial populations or enable rapid adaptation under stress, but they also raise the risk of deleterious mutations and cancer in multicellular organisms.

In software engineering, a mutator refers to a tool or component that automatically generates small alterations to a program's code, creating mutants for mutation testing. The goal is to evaluate the effectiveness of a test suite by determining whether it detects, or kills, the mutants. Operators include arithmetic, logical, and constant replacement mutations; some frameworks distinguish weak and strong mutation testing.

In programming language design and software design, a mutator (setter) is a method that changes an object’s state by updating one of its fields. This contrasts with accessors (getters) that read state. Many languages provide language features for mutators, while design patterns or functional programming styles may encourage immutability and minimize or control mutator use.