Issue #17043 has been updated by marcandre (Marc-Andre Lafortune).

Status changed from Feedback to Rejected

>  But, it'd be great to be able to treat sets as predicate functions

Note that since Ruby 2.5, `Set#===` is an alias for `include?`, so you can do `ary.grep(Set[...])` for example.

> I'm curious if an officially blessed "Invokable" module might be a useful thing for the standard library.

Most of the standard library is being made available as separate gems (or removed altogether), so we're basically trying to reduce the standard library, not extend it. Thanks for enquiring though.

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Feature #17043: Invokable module for custom Proc-like objects 
https://bugs.ruby-lang.org/issues/17043#change-86691

* Author: delonnewman (Delon Newman)
* Status: Rejected
* Priority: Normal
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Ruby beautifully integrates Functional and Object-Oriented Programming, and there's more moving in the direction of supporting Functional Programming. A generalization of the Proc interface would enable users to integrate functional approach into their classic OOP design patterns. One of the obvious examples would be "Command" objects.

Also, generic structures, which Ruby has great support for. Hash now has `to_proc`.  But, it'd be great to be able to treat sets as predicate functions.

I've put together a prototype that I've found useful in my own work here: https://github.com/delonnewman/invokable.

It works like Enumerable; it can be included in any class that implements a `call` method. Then you get `to_proc`, `curry`, `<<` and `>>` for right and left composition, and `memoize`. More could be added. If you include `Invokable::Command`, you can treat your "Command" object as an automatically curried function.




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