References

A reference (&) is an alias. Once initialized, it is the variable it refers to.

• Difference from Pointers: Pointers can be nullptr or reassigned to point elsewhere. References must be initialized and cannot be changed to refer to something else.
• HPC Context: We use const T& (const reference) to pass large structs to functions. This avoids copying the entire object (saving cache and cycles) while promising not to modify it (const).

Pass-by-Value vs. Pass-by-Reference:

• void func(std::vector<int> v): Copies the entire vector (Slow).
• void func(std::vector<int>& v): Passes the address (Fast).