Questions re Method#to_proc


#1

Hello all,

Some things are unclear to me about Method#to_proc. I understand the
following:

plus = 12.method("+")
p plus.call(13) # prints 25

newplus = plus.unbind.bind(20)
p newplus.call(13) # prints 33

Although the usefulness of this eludes me :slight_smile:

However, this:

plus_proc = plus.to_proc
p plus_proc.call(10) # prints 10

Is unclear…

  1. How does it work ?
  2. What does it mean for a Proc to be bound to an object ?
  3. Can someone provide an example where it is useful ?
  4. Have the ‘bind’ and ‘unbind’ methods of Method / UnboundMethod
    anything in common with Proc#binding or the Binding class ?
  5. Have Proc#binding and the Binding class anything in common ? How
    about Kernel#binding ?

Additionally, the following, IMHO demostrates a very surprising and
unnatural behavior of to_proc:

def foo(arr)
puts “Got an array with #{arr.length} elements”
end

works correctly

foo([4, 5, 6])

foo_proc = method(:foo).to_proc

throws an ArgumentError: 3 for 1

foo_proc.call([4, 5, 6])

works correctly

foo_proc.call([[4, 5, 6]])

The Proc created by to_proc is obviously different from the original
method, since it “folds” its arguments into an array. I guess there
will be even more problems when the method receives more than one array
as an argument.
How should this be handled correctly ?

Thanks in advance


#2

Hi,

In message “Re: questions re Method#to_proc”
on Tue, 18 Apr 2006 17:39:51 +0900, Eli B. removed_email_address@domain.invalid
writes:

|Additionally, the following, IMHO demostrates a very surprising and
|unnatural behavior of to_proc:
|
|def foo(arr)
| puts “Got an array with #{arr.length} elements”
|end
|
|# works correctly
|foo([4, 5, 6])
|
|foo_proc = method(:foo).to_proc
|
|# throws an ArgumentError: 3 for 1
|foo_proc.call([4, 5, 6])
|
|# works correctly
|foo_proc.call([[4, 5, 6]])

This issue will be solved in the future version (1.9), which should
give you the following result:

Got an array with 3 elements
Got an array with 3 elements
Got an array with 1 elements

						matz.

#3

Yukihiro M. wrote:

|# works correctly
|foo([4, 5, 6])
|
|foo_proc = method(:foo).to_proc
|
|# throws an ArgumentError: 3 for 1
|foo_proc.call([4, 5, 6])
|
|# works correctly
|foo_proc.call([[4, 5, 6]])

This issue will be solved in the future version (1.9), which should
give you the following result:

Got an array with 3 elements
Got an array with 3 elements
Got an array with 1 elements

  					matz.

Thanks, Matz.

By the way, when is 1.9 due ?


#4

Hi,

In message “Re: questions re Method#to_proc”
on Thu, 20 Apr 2006 02:14:00 +0900, Eli B. removed_email_address@domain.invalid
writes:

|By the way, when is 1.9 due ?

You can fetch it from CVS right now.

						matz.