Why are php array keys case sensitive?

Question

While looking through some code and attempting to fix some issues I came to a question. Why are PHP array keys case sensitive? It would seem beneficial to have

$array = array(
   "Key"=>"Value",
   "key"=>"Value",
)

be the same key. Can someone explain to me the benefit of having those two keys separated?

Answer 1

PHP arrays are implemented with hash tables. The way a hash table works, to first order: it hashes the input and uses that as an index to find the right memory location to insert an object.

Now imagine your arrays are case-insensitive. Rather than doing a single hash lookup, you now have to do 2^(length of your string) hash lookups. Furthermore, of these locations, which one do you choose? Suddenly your elegant, simple hash table has become much more complicated, both computationally and in its implementation.

Furthermore, in most other languages, Key and key are treated differently. PHP certainly doesn't always adhere to the principle of least surprise, but in this case it does -- and that's how it should be.

As other users have pointed out, this behavior is easy to obtain if you desire it: simply convert your keys to lowercase before inserting and/or referencing them.