What are the Limitations of Valid Character Types for PHP Array Keys?

Valid Characters in PHP Array Keys

Question:

When constructing PHP arrays, can you use any character in the key? Are there any limitations?

Answer:

According to the PHP manual, the following rules apply to array keys:

• Keys can be integers or strings.
• Keys containing valid integers will be cast to integers.
• Floats will be cast to integers, with the fractional part being truncated.
• Booleans will be cast to 1 (for true) or 0 (for false).
• Null will be cast to an empty string.
• Arrays and objects cannot be used as keys and will result in a warning.

Regarding strings, the manual states that a string represents a series of characters, where a character is the same as a byte. This means that PHP supports a 256-character set, effectively using binary data.

Therefore, in summary, any string can be a valid array key, including any binary data (up to 2GB). Here are some unconventional but valid examples:

<code class="php">$w = array(
    chr(0) => 'null byte?',
    chr(rand(0, 255)) => 'random byte?'
);
var_dump($w);</code>

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