Should Pass-by-Value Be the Default for Large Objects in C 11?

Is Pass-by-Value a Prudent Default in C 11?

Traditionally, passing by value in C has been regarded as inefficient for large objects, prompting programmers to opt for passing references instead. However, with the advent of C 11 and its introduction of rvalue references and move constructors, the feasibility of pass-by-value for large objects has resurfaced.

The Case for Pass-by-Value as Default

Dave Abrahams argues that copying arguments inside functions should be avoided and suggests instead passing them by value, allowing the compiler to handle the copying. This strategy simplifies code and enables the caller to use functions with both lvalues and rvalues, minimizing the work required. In the code example provided, passing by reference would necessitate two separate overloads to achieve the same functionality.

Considerations for Custom Objects

While pass-by-value is a reasonable default for value-type objects (e.g., std::vector), it may not be optimal for custom objects that require complex copy semantics or where pointers or references are involved. In such cases, passing by reference to const remains a suitable choice to prevent unintentional modification of the object.

Improved Code Safety and Performance

Implementing valuable constructors, as shown in the example, ensures that copies of large objects are moved rather than copied, optimizing performance. Additionally, passing by value eliminates the need for complex ownership and memory management considerations, enhancing code safety.

Conclusion

In C 11, pass-by-value can be a logical default for large objects if copying is necessary within the function body. This approach simplifies code, allows for flexible input handling, and leverages compiler optimizations for improved performance. However, custom objects should be evaluated on a case-by-case basis, and passing by reference to const may remain the preferred option for scenarios involving complex copy semantics or potential modifications.

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