constcorrect

Constcorrect, or const-correctness, is a software design principle that uses a language’s const qualifiers to express and enforce immutability. It aims to ensure that objects not intended to change are not modifiable through their interfaces, and that code only alters state when explicitly allowed. The concept is most closely associated with C++, but similar ideas exist in other languages with readonly, immutable, or final qualifiers.

Key practices include declaring member functions that do not modify object state as const, using const references or pointers for parameters, and returning values or references in a way that prevents unintended modification. Const-correct code distinguishes between logical constness and physical constness: a class may present a const interface while performing internal mutations via mutable members or through cached data. This separation helps maintain clean APIs and predictable behavior.

Example:

class Data {

public:

int getValue() const { return value; }

void setValue(int v) { value = v; }

private:

int value;

};

In this example, getValue is a const member function and can be called on const Data objects, whereas setValue cannot.

Benefits of const-correctness include earlier error detection by the compiler, clearer expression of intent, and enabling certain compiler optimizations. It also improves API design by allowing functions to operate on const objects without risking unintended modifications.

Common pitfalls include overusing const, which can complicate design, and relying on const_cast or mutable to bypass constness, which can undermine safety. Const-correctness is a foundational practice in many C++ codebases and libraries, contributing to safer, more maintainable interfaces, though it does not by itself guarantee thread-safety.