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6/30/2026
The Array Bug That Looks Different in PHP, Python, and JavaScript (But Is Really the Same Bug)

The Array Bug That Looks Different in PHP, Python, and JavaScript (But Is Really the Same Bug)

Short summary

PHP copies arrays by default while Python and JavaScript share references—a critical distinction that causes subtle, hard-to-debug mutations when you switch languages. This tutorial breaks down the semantics of each language with code examples and a reference table. Master copy-on-write semantics and explicit copying strategies to eliminate this entire class of bug.

  • •PHP copies arrays by default; Python and JavaScript share references
  • •Understand mutation behavior and copy semantics for each language
  • •Use explicit copying (& in PHP, [:]/deepcopy in Python, [...]/structuredClone in JS) to prevent silent bugs

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