rfc:namespace_scoped_declares

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rfc:namespace_scoped_declares [2017/12/11 13:19] – nikicrfc:namespace_scoped_declares [2022/01/25 18:22] (current) – Move to inactive ilutov
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   * Author: Nikita Popov <nikic@php.net>   * Author: Nikita Popov <nikic@php.net>
   * Proposed PHP version: PHP 7.3   * Proposed PHP version: PHP 7.3
-  * Status: Under Discussion+  * Status: Inactive
   * PR: https://github.com/php/php-src/pull/2972   * PR: https://github.com/php/php-src/pull/2972
   * ML thread: http://externals.io/thread/326   * ML thread: http://externals.io/thread/326
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 This restriction is introduced for two reasons: Firstly, lack of such a restriction would imply that language behavior can silently change in the middle of a single file, which would be very confusing. Secondly, there are are significant implementational complexities associated with allowing this type of code due to limitations of specific declare directives. In particular the current implementation of ''strict_types'' only permits a consistent ''strict_types'' value for a whole file. Lifting the declare-consistency requirement would require changing the ''strict_types'' implementation to support this and, more importantly, commitment to support this for all future declare directives we introduce, which may be non-trivial. This restriction is introduced for two reasons: Firstly, lack of such a restriction would imply that language behavior can silently change in the middle of a single file, which would be very confusing. Secondly, there are are significant implementational complexities associated with allowing this type of code due to limitations of specific declare directives. In particular the current implementation of ''strict_types'' only permits a consistent ''strict_types'' value for a whole file. Lifting the declare-consistency requirement would require changing the ''strict_types'' implementation to support this and, more importantly, commitment to support this for all future declare directives we introduce, which may be non-trivial.
 +
 +==== Supported declare directives ====
 +
 +Currently PHP supports three declare directives, ''ticks'', ''strict_types'' and ''encoding''.
 +
 +''namespace_declare()'' does not support ''encoding'' and will generate an ''Error'' if it is specified. The reason is that ''encoding'' has very special semantics, and requires the directive to be resolved already at parse-time, so that the lexer behavior may be influenced. At the point where the first namespace is encountered, it may already be too late to act on this directive.
 +
 +For ''ticks'' the passed value must be a non-negative integer, otherwise an ''Error'' is thrown.
 +
 +For ''strict_types'' the passed value must be integer ''0'' or ''1'', otherwise an ''Error'' is thrown.
  
 ==== Open Question: Handling of unknown directives ==== ==== Open Question: Handling of unknown directives ====
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 If we go for throwing a warning here, it might be beneficial to add a ''supports_declare()'' function, which allows you to determine whether a certain declare directive is supported, without resorting to a PHP version check (which would likely be unreliable with regard to alternative PHP implementations). If we go for throwing a warning here, it might be beneficial to add a ''supports_declare()'' function, which allows you to determine whether a certain declare directive is supported, without resorting to a PHP version check (which would likely be unreliable with regard to alternative PHP implementations).
 +
 +==== Open Question: Introspection functionality ====
 +
 +It might be useful to also provide a mechanism to retrieve the active namespace-scoped declares at runtime, e.g. using a ''get_namespace_declares()'' function. One could either make this return the declarations for all namespaces exactly as given, or return the computed declarations for a specific namespace. I'm not sure what the specific use-case for this kind of introspection functionality would be, though.
  
 ==== Implementation considerations ==== ==== Implementation considerations ====
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   * Resolve open question "Handling of unknown directives"   * Resolve open question "Handling of unknown directives"
-  * Consider adding some introspection functionality, such as ''get_namespace_declares()'' +  * Resolve open question "Introspection functionality"
-  * Investigate whether this mechanism can support the ''encoding'' directive, which is a lot more magic than the rest.+
rfc/namespace_scoped_declares.1512998386.txt.gz · Last modified: 2017/12/11 13:19 by nikic

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