Does Pass-by-Reference Actually Improve Performance in PHP?

Pass-by-Reference and Performance in PHP: Myth Debunked

In PHP, passing function parameters by reference has been a subject of debate, with some speculating it may affect performance. While using references allows functions to modify variables outside their scope, it doesn't necessarily enhance speed.

Copy On Write Mechanism

PHP employs a "Copy On Write" mechanism to minimize object and array copies. Only when these objects are modified, are they copied. Therefore, for functions that merely use parameters without making changes, the behavior is akin to pass-by-reference.

Performance Analysis

To clarify misconceptions, performance tests were conducted with a function that either reads or changes a 20 kB string parameter. The results were surprising:

• Function Reading/Using Parameter:

  • Pass by value: 0.12065005 seconds
  • Pass by reference: 1.52171397 seconds

• Function Writing/Changing Parameter:

  • Pass by value: 1.52223396 seconds
  • Pass by reference: 1.52388787 seconds

Inferences

The tests reveal that passing by value is consistently faster than pass-by-reference for both reading and modifying parameters. This suggests that PHP's Copy On Write mechanism isn't bypassed or optimized for pass-by-reference.

Conclusion

Contrary to popular belief, using pass-by-reference in PHP does not improve performance. For functions that don't alter parameter values, copying is negligible. However, if parameter modifications are necessary, pass-by-reference and pass-by-value have nearly identical performance characteristics. Therefore, it's crucial to use pass-by-reference only when modifying variables outside the function's scope, as it was originally intended for.

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