PHP Data Types

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TL;DR

Explanation

PHP is dynamically typed with eight primitive types: bool, int, float (double), string, array, object, callable, and null. PHP 8.0 formalised mixed (any type) and never (no return). Type coercion rules are nuanced: '1' == 1 is true, '0' == false is true, but null == false and null == 0 are also true. PHP 8.0 changed 0 == 'foo' to false (was true in PHP 7). Typed properties (PHP 7.4+), union types (8.0), and strict_types enforce types at runtime. Understanding coercion rules is critical for security (authentication bypass via type juggling) and correctness.

Common Misconception

Why It Matters

Common Mistakes

• Not enabling strict_types=1 — PHP silently coerces '42' to 42 for int parameters without it.
• Using == to compare values of different types — '0' == false == null == 0 in loose comparison.
• Forgetting that array is a first-class type in PHP, not an object — json_encode behaviour differs.
• Using float for currency — floating-point precision errors accumulate; use integer cents or bcmath.

Code Examples

// Loose comparison type confusion:
var_dump(0 == 'a');     // true in PHP 7, false in PHP 8 — changed!
var_dump('' == false);  // true
var_dump('0' == false); // true
var_dump(0 == null);    // true
// Use === always for predictable comparisons

// PHP 8 scalar types:
\$int   = 42;          // PHP_INT_MAX = 9223372036854775807 on 64-bit
\$float = 3.14;        // IEEE 754 double — avoid for money (use int cents)
\$str   = 'hello';     // byte string — mb_* functions for Unicode
\$bool  = true;

// Compound:
\$arr   = [1, 'two', 3.0];              // ordered map
\$assoc = ['key' => 'value'];
\$obj   = new stdClass();
\$null  = null;

// PHP 8 type system additions:
// union: int|string
// intersection: Iterator&Countable (8.1)
// never, void, mixed
// Enums with backed types (8.1)

// Type juggling changes in PHP 8:
var_dump(0 == 'foo'); // false in PHP 8 (was true in PHP 7)
var_dump(0 == '');    // false in PHP 8 (was true in PHP 7)

References

• ↗ https://www.php.net/manual/en/language.types.php

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