Is Passing by Reference Faster in PHP (>=5.0)?
Despite the primary purpose of pass-by-reference in PHP being variable manipulation outside the function's scope, one might speculate if it also affects performance. PHP employs Copy On Write to optimize object and array copying, which should eliminate the need for pass-by-reference for parameters that remain unchanged.
Performance Comparison
To determine the performance impact, an experiment was conducted with 100,000 function calls, passing a 20 kB string as a parameter. Two scenarios were tested:
- Function that reads/uses the parameter
- Function that writes/modifies the parameter
Results
-
Pass by Value vs. Reference for Reading/Using Parameters:
- Pass by value: 0.12065005 seconds
- Pass by reference: 1.52171397 seconds
-
Pass by Value vs. Reference for Writing/Modifying Parameters:
- Pass by value: 1.52223396 seconds
- Pass by reference: 1.52388787 seconds
Conclusions
- Passing by value is consistently faster than pass-by-reference.
- For functions that modify the parameter's value, there is no practical performance difference between pass-by-value and pass-by-reference.
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