When to Choose Pass by Value vs Pass by Rvalue Reference in C ?

Pass by Value vs Pass by Rvalue Reference

Deciding between pass by value or pass by rvalue reference for function parameters depends on several factors.

Pass by Value

• (Widget w)

  • Creates a copy of the input parameter, leaving the original unchanged.
  • Involves an implicit copy operation, which can be inefficient for large or complex objects.
  • Assumes ownership of the parameter, even if it does not modify it.

Pass by Rvalue Reference

• (Widget&& w)

  • Forcibly initializes the parameter with an rvalue (e.g., an expiring temporary object), preventing a copy operation.
  • Requires explicit declaration of copies using std::move when the caller desires a copy.
  • Disables any changes in the return value being reflected in the caller's copy.

Key Differences

• Copy Ownership: Pass by value mandates that the parameter must be copied, while pass by rvalue reference allows the function to move the parameter, eliminating an extra move constructor call in some cases.
• Interface Semantics: Rvalue references indicate that the function intends to take ownership of the value and is not responsible for its continued existence.
• Efficiency: Pass by rvalue reference can be more efficient in cases where the caller does not need a copy of the input object.

Choosing the Correct Method

Use pass by value when:

• The function needs a copy or modified version of the input object.
• The input object is small or inexpensive to copy.

Use pass by rvalue reference when:

• The function needs to take ownership and modify the input object.
• The input object is large or expensive to copy.
• The caller does not require a copy of the input object.

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