Does Pass-by-Reference in PHP Enhance or Impede Performance?

Performance Implications of Pass-by-Reference in PHP

In PHP, function parameters can be passed by reference, denoted by an ampersand (&) before the parameter. While this concept is primarily used to allow functions to modify variables outside their scope, some have questioned its potential performance impact.

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

PHP employs Copy On Write (COW) to minimize copying of objects and arrays. This process ensures that the original data is shared between variables until any of them attempt to modify it. However, it raises the question of whether pass-by-reference short-circuits this COW logic, thereby enhancing performance.

Comparative Benchmark Tests

To ascertain the performance implications, tests were conducted with two scenarios: functions that (A) only read the parameter and (B) modify the parameter. The parameter was a string of 20 kB, and the function was called 100,000 times in each scenario.

Results

For scenario A (read-only function):

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

For scenario B (write/modify function):

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

Conclusions

Based on these results, it can be concluded that:

1. Pass-by-Value is Always Faster: In both scenarios, passing the parameter by value proved to be significantly faster than passing it by reference for read-only operations.
2. COW is Not Short-Circuited: Even though the tests confirmed that COW is active for passing by value, it is not circumvented when passing by reference for write operations. The performance difference between these two approaches for modifying parameters is negligible.

The above is the detailed content of Does Pass-by-Reference in PHP Enhance or Impede Performance?. For more information, please follow other related articles on the PHP Chinese website!