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Date: Tue, 23 Feb 2021 12:21:24 +0100
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To: PHP internals <internals@lists.php.net>
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Subject: Avoiding enum reserved keyword
From: nikita.ppv@gmail.com (Nikita Popov)

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Hi internals,

I'm a bit concerned about the addition of the "enum" reserved keyword as
part of https://wiki.php.net/rfc/enumerations. The problem is that there
are quite a few existing enum libraries (such as
https://github.com/myclabs/php-enum) that define an Enum class. While the
implementation of enums in PHP 8 obsoletes these libraries, it still
constitutes a migration problem, especially for libraries supporting more
than one PHP version.

I don't believe that the keyword is strictly necessary: We can recognize
enum declarations as T_STRING T_STRING, where the former is checked to be
equal to "enum" by the parser. It so happens that this is syntactically
unambiguous at this time. We may be forced to introduce the keyword at a
later time, if it becomes ambiguous.

Another possibility would be to recognize T_ENUM in the lexer, but only if
it is followed by whitespace and an identifier. This would possibly be
friendlier for tooling using token_get_all(). It would not permit comments
in between the tokens though.

Thoughts?

Regards,
Nikita

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