Why does C++ disallow anonymous structs?

The primary reason C++ does not allow anonymous structures is rooted in its design philosophy and the need for type safety. C++ emphasizes type clarity and scope management, which helps improve code maintainability and reduce potential errors.

Type Safety and Clarity

As a strongly typed language, C++ emphasizes type clarity. The use of anonymous structures may lead to ambiguous types, which contradicts C++'s design principles. In C++, every variable and structure requires explicit type definition, which helps the compiler perform type checking and reduce runtime errors.

Scope and Lifetime Management

C++'s scope rules require each object to have a well-defined lifetime and scope, which aids in effective resource management. Anonymous structures may result in unclear scope boundaries, thereby complicating resource management.

Maintainability and Readability

In large software projects, code maintainability and readability are crucial. Structures with explicit names make the code more understandable and maintainable. Anonymous structures may make it difficult for readers to understand the purpose and meaning of the structure, especially when used across different contexts.

Compatibility with C

Although C supports anonymous structures, C++ introduces stricter requirements and more complex features, such as classes, inheritance, and templates. When adding these features, it is necessary to ensure all features operate within the framework of type safety and C++'s design philosophy. The introduction of anonymous structures may conflict with these features.

Consider the following C++ code snippet:

cpp
struct {
    int x;
    double y;
} position;

position.x = 10;
position.y = 20.5;

This code is valid in C but invalid in C++, as C++ requires all types to have explicit definitions. To achieve similar functionality in C++, we can write:

cpp
struct Position {
    int x;
    double y;
};

Position position;
position.x = 10;
position.y = 20.5;

In this example, using the explicitly named Position structure ensures compliance with C++ standards and enhances readability and maintainability.

In summary, C++ does not support anonymous structures primarily to maintain type clarity, improve code quality, and avoid potential programming errors.