Issue #7248 has been updated by marcandre (Marc-Andre Lafortune).

Priority changed from Normal to High

Thanks for the answers.

So, the public API of Lazy.new has the following issues:

* not documented
* should require a block but doesn't
* accepts a method name & arguments which aren't really usable
* has a misleading "inspect"

Moreover, the only way for the user to create a lazy enumerator with a size is to subclass Lazy.

Here's what I propose as the official Lazy.new documentation and API:

    Lazy.new(obj, size=nil) { |yielder, *values| ... }

    Creates a new Lazy enumerator. When the enumerator is actually enumerated
    (e.g. by calling #force), +obj+ will be enumerated and each value passed
    to the given block. The block can yield values back using +yielder+.
    For example, to create a method +filter_map+ in both lazy and
    non-lazy fashions:

        module Enumerable
          def filter_map(&block)
            map(&block).compact
          end
        end

        class Enumerator::Lazy
          def filter_map
            Lazy.new(self) do |yielder, *values|
              result = yield *values
              yielder << result if result
            end
          end
        end

        (1..Float::INFINITY).lazy.filter_map{|i| i*i if i.even?}.first(5)
            # => [4, 16, 36, 64, 100]

Does this seem acceptable to you?

We should also change the result of the 'inspect' method for these user created lazy enumerators to remove the 'each', i.e:

    (1..Float::INFINITY).lazy.filter_map{|i| i*i if i.even?}.inspect
    # => #<Enumerator::Lazy: #<Enumerator::Lazy: 1..Infinity>>

If we want to provide an easy way to provide more info in the inspect, we could add extra parameters, but they shouldn't be used when iterating, only for inspection...

> BTW, I have a question. Document of to_enum says "see Enumerator#size=" but there is no such method. Is it a typo?

Typo fixed, thanks.


----------------------------------------
Bug #7248: Shouldn't Enumerator::Lazy.new be private?
https://bugs.ruby-lang.org/issues/7248#change-35397

Author: marcandre (Marc-Andre Lafortune)
Status: Assigned
Priority: High
Assignee: marcandre (Marc-Andre Lafortune)
Category: core
Target version: 2.0.0
ruby -v: ruby 2.0.0dev (2012-10-29 trunk 37380) [x86_64-darwin10.8.0]


Is there a reason why Enumerator::Lazy.new is not private?

Lazy enumerators should be created with `Enumerable#lazy`. Moreover, there is no doc, and it can give unexpected results too.


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