What are the Benefits of Using \'= default\' in C 11?

Exploring the New Syntax ""= default"" in C 11

In C 11, the ""= default"" syntax was introduced to provide a concise way of defining default constructors, copy/move constructors, and destructors. While it may seem redundant at first glance, using ""= default"" offers several benefits.

Specifying the Default Behavior Precisely

The ""= default"" syntax explicitly declares that the default constructor should be generated by the compiler, ensuring that it behaves as expected. By contrast, omitting the ""= default"" syntax leaves room for ambiguity, as the behavior of the implicitly generated default constructor is not always clear.

Maintaining Aggregate and Trivial Properties

Default constructors that are declared explicitly as ""= default"" preserve the aggregate and trivial properties of a class. An aggregate is a data type that only contains fundamental data types (e.g., integers, floats), while a trivial class is a class that has a trivial constructor and destructor. By using ""= default"," you explicitly declare that the default constructor will not initialize any data members, preserving these properties.

Consistency and Code Readability

Using ""= default"" for all special member functions (constructors, copy/move constructors, destructors) promotes consistency and enhances code readability. By explicitly stating your intention to use the default behavior, you avoid confusion that could arise from omitting these declarations.

An Example

Consider the following code snippet:

struct S {
    int a;
    S(int aa) : a(aa) {}
    S() = default;
};

In this example, the ""= default"" syntax is used to explicitly declare a default constructor that will not initialize the a data member. This ensures that S remains an aggregate type, which may be important for performance optimizations.

Conclusion

While the ""= default"" syntax may initially seem unnecessary, closer examination reveals its significance in ensuring precise behavior, maintaining aggregate and trivial properties, and promoting code readability.

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