From: "headius (Charles Nutter)" <headius@...>
Date: 2012-11-13T10:57:42+09:00
Subject: [ruby-core:49274] [ruby-trunk - Feature #4085] Refinements and nested methods
Issue #4085 has been updated by headius (Charles Nutter).
Well, I have some bad news.
I have spent some time trying to find a reasonable way to implement refinements in JRuby, and without reducing the feature set it's simply not possible to do without global (and sometimes terrible) impact to general application performance.
At this point I'm largely of the opinion that pure-lexical, syntactical refinements are the way to go. And there are several reasons for it:
* Dynamic refinements have far-reaching impact, both peformance-wise and "understandability" of the code. It's both hard (or impossible) to optimize and hard (or impossible) to reason about.
* Syntactic/lexical refinements are nearly self-explanatory in code. Currently, when you look at a piece of code with method calls (and constant lookup, as well), you can reason about it in terms of the enclosing classes/modules and basically know what it will call. Monkeypatching can obscure the eventual method called, but every piece of code everywhere will still call the same method. With dynamic refinements, it's impossible to look at a piece of code and the classes involved and know what method will be called, because it can change arbitrarily at runtime.
* The current refinements are poorly specified and have only been explored in a very limited way. This is of *great* concern to me. There are a huge number of potential edge cases, ranging from abuse of the module_eval feature to reopening existing refinements (which essentially just makes monkeypatching harder to discover), and implementation-wise there has not been enough exploration of how it will affect current and future performance of Ruby. We need more time to define what refinements should do in terms of what users want and what's reasonable from a language-design perspective.
I would support the idea of pure lexical/syntactic refinements of the following form, but I don't see a way to support the features of the current refinements implementation reasonably on any VM.
module Foo
class Quux
using Bar, Baz
def blah
'abc'.efg # refined
end
end
def blah2
'asdf'.qwer # unrefined
end
end
end
----------------------------------------
Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-32829
Author: shugo (Shugo Maeda)
Status: Assigned
Priority: Normal
Assignee: shugo (Shugo Maeda)
Category: core
Target version: 2.0.0
=begin
As I said at RubyConf 2010, I'd like to propose a new features called
"Refinements."
Refinements are similar to Classboxes. However, Refinements doesn't
support local rebinding as mentioned later. In this sense,
Refinements might be more similar to selector namespaces, but I'm not
sure because I have never seen any implementation of selector
namespaces.
In Refinements, a Ruby module is used as a namespace (or classbox) for
class extensions. Such class extensions are called refinements. For
example, the following module refines Fixnum.
module MathN
refine Fixnum do
def /(other) quo(other) end
end
end
Module#refine(klass) takes one argument, which is a class to be
extended. Module#refine also takes a block, where additional or
overriding methods of klass can be defined. In this example, MathN
refines Fixnum so that 1 / 2 returns a rational number (1/2) instead
of an integer 0.
This refinement can be enabled by the method using.
class Foo
using MathN
def foo
p 1 / 2
end
end
f = Foo.new
f.foo #=> (1/2)
p 1 / 2
In this example, the refinement in MathN is enabled in the definition
of Foo. The effective scope of the refinement is the innermost class,
module, or method where using is called; however the refinement is not
enabled before the call of using. If there is no such class, module,
or method, then the effective scope is the file where using is called.
Note that refinements are pseudo-lexically scoped. For example,
foo.baz prints not "FooExt#bar" but "Foo#bar" in the following code:
class Foo
def bar
puts "Foo#bar"
end
def baz
bar
end
end
module FooExt
refine Foo do
def bar
puts "FooExt#bar"
end
end
end
module Quux
using FooExt
foo = Foo.new
foo.bar # => FooExt#bar
foo.baz # => Foo#bar
end
Refinements are also enabled in reopened definitions of classes using
refinements and definitions of their subclasses, so they are
*pseudo*-lexically scoped.
class Foo
using MathN
end
class Foo
# MathN is enabled in a reopened definition.
p 1 / 2 #=> (1/2)
end
class Bar < Foo
# MathN is enabled in a subclass definition.
p 1 / 2 #=> (1/2)
end
If a module or class is using refinements, they are enabled in
module_eval, class_eval, and instance_eval if the receiver is the
class or module, or an instance of the class.
module A
using MathN
end
class B
using MathN
end
MathN.module_eval do
p 1 / 2 #=> (1/2)
end
A.module_eval do
p 1 / 2 #=> (1/2)
end
B.class_eval do
p 1 / 2 #=> (1/2)
end
B.new.instance_eval do
p 1 / 2 #=> (1/2)
end
Besides refinements, I'd like to propose new behavior of nested methods.
Currently, the scope of a nested method is not closed in the outer method.
def foo
def bar
puts "bar"
end
bar
end
foo #=> bar
bar #=> bar
In Ruby, there are no functions, but only methods. So there are no
right places where nested methods are defined. However, if
refinements are introduced, a refinement enabled only in the outer
method would be the right place. For example, the above code is
almost equivalent to the following code:
def foo
klass = self.class
m = Module.new {
refine klass do
def bar
puts "bar"
end
end
}
using m
bar
end
foo #=> bar
bar #=> NoMethodError
The attached patch is based on SVN trunk r29837.
=end
--
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