Daniel Schierbeck
12/9/2005 6:56:00 PM
beng wrote:
> I've made good use of this idiom recently, and wanted to share it.
>
> Once this code is active, any method named with a "_c" suffix is
> automatically cached. The method is assumed to follow a simple
> contract: It performs no side-effects / mutations, and it's arguments
> properly implement "Object.hash".
>
> This is specifically useful for expensive but functional calculations.
> Enjoy!
>
> --Ben (b@gimpert.com)
>
> # <code>
> class Class
>
> alias old_new new
> def new(*args, &block)
> Class.defc_wrap(old_new(*args, &block))
> end
>
> def Class.defc_wrap(obj)
> klass = obj.class
> defc_methods = obj.methods.select { |n| n =~ /_c$/ }
> defc_methods.each do |name|
> meth = obj.method(name)
> wrapped_name = Class.defc_next_name(klass)
> cache = klass.class_eval("@#{wrapped_name} = {}")
> wrapper = Proc.new do |*args_a|
> arg_hash = args_a.hash
> if cache.has_key?(arg_hash)
> cache[arg_hash]
> else
> cache[arg_hash] = meth.call(*args_a)
> end
> end
> klass.send(:alias_method, wrapped_name, name)
> klass.send(:define_method, name, wrapper)
> end
> obj
> end
>
> def Class.defc_next_name(obj)
> klass = obj.class
> i = 1
> i += 1 while obj.respond_to?("_defc_#{i}") ||
> obj.instance_variables.member?("@_defc_#{i}")
> "_defc_#{i}"
> end
>
> end
> </code>
This is a touched-up version of your code.
class Class
alias_method :__new__, :new
def cached_method(*methods)
@cached_methods ||= []
@cached_methods += methods
@cached_methods.uniq!
end
def new(*args, &block)
obj = __new__(*args, &block)
klass = obj.class
@cached_methods ||= []
@cached_methods.each do |name|
meth = obj.method(name)
i = 1
while klass.instance_variables.member?("@_defc_#{i}")
i += 1
end
wrapped_name = "_defc_#{i}"
cache = klass.class_eval("@#{wrapped_name} = {}")
wrapper = Proc.new do |*args_a|
arg_hash = args_a.hash
if cache.has_key?(arg_hash)
cache[arg_hash]
else
cache[arg_hash] = meth.call(*args_a)
end
end
klass.send(:alias_method, wrapped_name, name)
klass.send(:define_method, name, wrapper)
end
return obj
end
end
class Klass
def foo; end
def bar; end
cached_method :foo, :bar
end