Re: [ ruby-Bugs-3565 ] Method object used as Object#instance_eval block doesn't work (as expected)

Hi,

In message "Re: [ ruby-Bugs-3565 ] Method object used as Object#instance_eval block doesn't work (as expected)"
    on Wed, 15 Feb 2006 19:05:03 +0900, H.Yamamoto <[e-mail]> writes:

|Fowarding.... (Ozgur Murat Homurlu)
|http://rubyforge.org/tracker/index.php?func=detail&aid=3565&group_id=426&atid=1698
|
|  Hello, 
|  Removing the argument which contains the receiver solves 
|  only part of the problem. The other part is instance_eval 
|  doesn't set the self to the receiver. What the code tries 
|  to do is running W#foo in the context of a (that is, in 
|  W#foo, self should be equal to a).

A method object is tightly bound to its receiver.  Even instance_eval
cannot rebind the bound receiver of a method object, mostly because
methods simply just don't work well with objects of other types,
unlike simple Proc objects written in Ruby.  For example, string
methods like #split expect their receiver to be strings, and no other
type.  If rebound is allowed they would just crash.

|  I know there are other 
|  techniques for this purpose but since Method objects can 
|  be converted to Proc objects and instance_eval runs Proc 
|  object given as a block in the context of the receiver  
|  (that is, self set to the receiver of instance_eval for 
|  the Proc), it's expected to be possible. 

Considering above reason, we have three choices: a) disallow invoking
instance_eval with a proc made from a method at all.  b) abandon
receiver rebinding for a proc made from a method.  c) add type checks
for the receivers in every methods, no matter who implemented.  these
checks could be source of bugs, and could slow down the interpreter a
lot.

I'd rather choose option b.  It's safe, fast, and inconsistency is
small.  As far as I can imagine, not many people try to rebind the
receiver of the bound method using instance_eval().

							matz.