Issue #10513 has been reported by Cliff Matthews.

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misc #10513: instance_eval yields the receiver, but is documented to yield no arguments
https://bugs.ruby-lang.org/issues/10513

* Author: Cliff Matthews
* Status: Open
* Priority: Low
* Assignee: Zachary Scott
* Category: doc
* Target version: 
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instance_eval yields the receiver, but is documented as yielding no arguments.

I searched the bug reports before writing this up and found bug #2476 which was closed with a message that contained "instance_eval yields the receiver in both 1.8 and 1.9. Unfortunately, a Proc object created by lambda raises ArgumentError when extra arguments are yielded in 1.9.".  However such behavior is not expected when the calling sequence is:
~~~
 *  call-seq:
 *     obj.instance_eval(string [, filename [, lineno]] )   -> obj
 *     obj.instance_eval {| | block }                       -> obj
~~~
This discrepancy surprised me, but once I realized what was going on I simply used instance_exec instead of instance_eval. All else equal, I would prefer for instance_eval to to not yield the receiver since I can pick up the receiver as self if I want to, but such a change could breaking existing code, so probably documenting the current behavior is better.

~~~
bash-3.2$ ruby --version
ruby 2.1.3p242 (2014-09-19 revision 47630) [x86_64-darwin14.0]
bash-3.2$ ./instance_eval
This is the lambda that *does* work.
arg = 32
self = 32
./instance_eval:6:in `block in <main>': wrong number of arguments (1 for 0) (ArgumentError)
	from ./instance_eval:17:in `instance_eval'
	from ./instance_eval:17:in `<main>'
~~~

---Files--------------------------------
instance_eval (561 Bytes)


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