Issue #10394 has been updated by Andrew Vit.


It might be confusing if such a thing only exists for Enumerator blocks and nothing else.

~~~ruby
["foo", "bar"].map.as_self { clear }
["foo", "bar"].tap.as_self { clear } # (not an Enumerator)
~~~

What would be the correct receiver in your proposal for the following example? What happens when the method is not defined in the block's "self" object?

~~~ruby
@members = ["foo", "bar"]
def transform_all
  @members.each.as_self { transform }
end
def transform
  raise "this one?"
end
~~~

A little bit related: #10095 (for the proposed syntax "as" vs. "as_self")

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Feature #10394: An instance method on Enumerator that evaluates the block under with self being the block variable.
https://bugs.ruby-lang.org/issues/10394#change-49595

* Author: Tsuyoshi Sawada
* Status: Feedback
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
----------------------------------------
**Background**

There has been desire to omit the `| |` and the explicit receiver in a block used with an enumerator or an enumerable. Currently, when the content of the block is a single method that takes no argument, symbol-to-proc is used with the `&` syntax so that:

~~~ruby
["foo", "bar"].map{|s| s.upcase}
~~~

can be written as:

~~~ruby
["foo", "bar"].map(&:upcase)
~~~

There has repeated been proposals (#8987, #9076, #10318) that express this desire to do this even when the block involves a method chain or a method with arguments like the following:

~~~ruby
["foo", "bar"].map{|s| s.concat("ber")}
["  foo ", "\tbar\n"].map{|s| s.strip.upcase}
~~~

Focus has been on modifying how a block is passed to the enumerable/enumerator, and there has not been consensus on how the syntax should be.


**Proposal**

Unlike the earlier proposals, I suggest that there should be an instance method on `Enumerator`, let's say `Enumerator#as_self`, that evaluates the block each time with `self` being the block variable that would be passed otherwise. With such method, the cases above would be written like this:

~~~ruby
["foo", "bar"].map.as_self{concat("ber")}
["  foo ", "\tbar\n"].map.as_self{strip.upcase}
~~~

This adds no modification to the syntax, it just requires a new method `Enumerator#as_self` to be implemented. I consider this method being along the lines of `Enumerator#with_index`, `Enumerator#with_object`; it intervenes between an enumerator (related to a block-taking method) and a block, and let the block-taking method work in a modified way.

It resembles `instance_eval`, but is different in that it assigns to `self` what would be a block variable (which changes for each iteration), instead of assigning the receiver.



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