Generics

Generics are a programming language feature that allows code to be written with placeholders for types. By parameterizing types and functions, generic constructs enable algorithms and data structures to operate on many different types while preserving type safety. The primary goals are to reduce code duplication, improve reusability, and catch type errors at compile time rather than at runtime.

A generic type or function declares one or more type parameters. At use, a concrete type substitutes the parameters. Depending on the language, the compiler may generate specialized code for each instantiation or employ a single representation with runtime checks. Type constraints can specify requirements for the type parameters, such as supporting certain operations. Type inference may allow omitting explicit type arguments.

There are practical differences across languages. Java uses type erasure, where generic type information is not retained at runtime. C# keeps reified generics, preserving type information at runtime. Languages like Rust and TypeScript perform compile-time checks and often generate specialized code or erase types after compilation. C++ relies on templates, which generate code at compile time for each instantiation and are more flexible but can lead to larger binaries.

Benefits of generics include stronger type safety, reduced duplication, and more abstract APIs that work across many types. Limitations involve added complexity, potential interaction with type constraints, and varying performance characteristics depending on implementation details such as erasure or specialization.

Common uses include generic collections, algorithms, and utilities that operate over any element type while maintaining compile-time type checks. See also parametric polymorphism, type constraints, and variance.