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Request for Comments: callable type hint

The problem

Frameworks have started to adopt Closures for callbacks, utilizing the 'Closure' typehint. That has an unfortunate sideeffect of requiring already-existing-methods to be wrapped into a closure calling that method. Additionally, the PHP documentation on closures indicates that the “Closure” class is considered an implementation detail, and may be subject to change in the future -- which means that typehinting on Closure may break in the future.

The solution

Introducing a callable typehint.

The typehint would allow a string with a function name, an array composed of classname/obj+methodname, and a closure.


Previous discussions

Discussion summary
  • The only arguments against the idea came from Stas, making the argument;
    • 'callable' is a data structure not unlike 'balanced binary tree' and 'readable file', and none of them make sense have as a part of the language syntax. They belong in userspace.
    • A “strict typing error” is hard to handle in user-space gracefully.
  • Everyone else seem to like the idea, so far.
  • As for the patch itself, Felipe pointed out that the patch is missing an method in ext/reflection to retrieve the typehint information.
  • Things to finalize:
    • Type name: documentation uses 'callback', not 'callable' as proposed
    • Are initializers allowed?
    • Does validation include visibility, as is_callable() does?
    • Reflection support
    • Arginfo support


  • June 7th 2011, Initial writeup
rfc/callable.1308183073.txt.gz · Last modified: 2017/09/22 13:28 (external edit)