PHP: rfc:php8:merge_symbol_tables

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====== RFC: Merge Symbol Tables ======
  * Version: 1.0
  * Date: 2015-05-16
  * Author: Levi Morrison <levim@php.net>
  * Status: Draft
  * First Published at: http://wiki.php.net/rfc/php8/merge_symbol_tables

===== Introduction =====
Currently we have symbol tables separate from each other based on kind. For instance, constants, functions, and classes/interfaces/traits all have their own tables. This allows us to use the same name for a constant, function, and a class all simultaneously:

<PHP>
const Symbol = 'symbol';
function symbol() {}
class Symbol {}
// no errors
</PHP>

This behavior is sometimes useful but prohibits other, more useful features such as the ability to use a function name as a callback without using strings:

<PHP>
// this looks for constant strlen, not function strlen:
array_map(strlen, ['hello', 'world']);

// must use the string:
array_map('strlen', ['hello', 'world']);
</PHP>

This makes it difficult to rename functions because it is more difficult to determine if a string is meant to be the function name or not compared to a symbolic usage. This RFC proposes to unify the constant, function, and class/interface/trait symbol tables into one.

===== Proposal =====
This RFC proposes to unify the constant, function, and class/interface/trait symbol tables into one.

===== Benefits =====
TODO

===== Backward Incompatible Changes =====
Any projects currently using the same name for different kinds of symbols will now get a redefinition error.

===== Proposed PHP Version(s) =====
This RFC targets PHP 8.0 or PHP 9.0 because of the backwards compatibility breaks.

===== RFC Impact =====
==== To Existing Extensions ====
TODO

==== To Opcache ====
Depending on the exact implementation it may be possible for opcache to work without any changes.

===== Open Issues =====
Constants are currently case sensitive while functions and classes are case insensitive. Should we unify the case sensitivity at the same time?

===== Future Scope =====
This sections details areas where the feature might be improved in future, but that are not currently proposed in this RFC.

===== Proposed Voting Choices =====
This RFC requires two-thirds of the votes to be in favor of logically unifying the symbol tables.

===== Patches and Tests =====
At this stage there is no patch.

===== References =====
Links to external references, discussions or RFCs
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