Feature #10394


An instance method on Enumerator that evaluates the block under with self being the block variable.

Added by sawa (Tsuyoshi Sawada) over 7 years ago. Updated about 3 years ago.

Target version:



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:

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

can be written as:

["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:

["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.


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:

["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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