Reading materials related to the PHP internals or performance.
- Disproving the Single Quotes Myth - An article about performance of single and double quoted strings.
- How Big Are PHP Arrays (And Values) Really? - An article about array internals.
- How Foreach Works - A detailed StackOverflow answer about foreach.
- How Long is a Piece of String - An article about string internals.
- PHP Evaluation Order - An article about evaluation order in PHP.
- PHP Internals Book - An online book about PHP internals, written by three core developers.
- PHP RFCs - The home of PHP RFCs (Request for Comments).
- Print vs Echo, Which One is Faster? - An article about print and echo performance.
- The PHP Ternary Operator. Fast or Not? - An article ternary performance.
- Understanding OpCodes - An article about opcodes.
- When Does Foreach Copy? - An article about the internals of foreach.
- Why Objects (Usually) Use Less Memory Than Arrays - An article about object and array internals.
- You're Being Lied To - An article about internal ZVALs.