From: ruby-core@... Date: 2019-09-03T04:03:28+00:00 Subject: [ruby-core:94752] [Ruby master Feature#15901] Enumerator::Lazy#eager Issue #15901 has been updated by marcandre (Marc-Andre Lafortune). knu (Akinori MUSHA) wrote: > > I'd also alias Enumerator#eager to #itself. > > Could you elaborate on why? Are you thinking of situations where lazy and eager enumerators are mixed? Yes, I was thinking of a method accepting a potentially lazy enumerator. It would be to avoid having to write `enum = enum.eager if enum.respond_to?(:eager)` and simply calling `enum.eager` no matter if the argument is eager or not. It's in the same way as `Enumerator::Lazy#lazy` is an alias to `itself`. I don't except it to be very useful though, lazy enumerators are probably rare and not often mixed with eager enumerators, so it might be premature. I just think the extra cognitive load is basically zero. ---------------------------------------- Feature #15901: Enumerator::Lazy#eager https://bugs.ruby-lang.org/issues/15901#change-81369 * Author: knu (Akinori MUSHA) * Status: Open * Priority: Normal * Assignee: matz (Yukihiro Matsumoto) * Target version: ---------------------------------------- There are cases where you want to create and pass a normal Enumerable object to a consumer where the methods like map and select are expected to return an array, but the calculation would be so space costly without using Enumerator::Lazy because of intermediate arrays. In such cases, you would want to chain `lazy` and calculation methods like `flat_map` and `select`, then convert the lazy enumerator back to a normal Enumerator. However, there is no direct method that converts a lazy Enumerator to an eager one, because the` to_enum` method returns a lazy Enumerator when the receiver is a lazy Enumerator. So, I propose this `eager` method as the missing piece for the said use case. Here's the rdoc from the attached patch. ```C /* * call-seq: * lzy.eager -> enum * * Returns a non-lazy Enumerator converted from the lazy enumerator. * * This is useful where a normal Enumerable object needs to be * generated while lazy operation is still desired to avoid creating * intermediate arrays. * * enum = huge_collection.lazy.flat_map(&:children).reject(&:disabled?).eager * enum.map {|x| ...} # an array is returned */ ``` ---Files-------------------------------- 0001-Implement-Enumerator-Lazy-eager.patch (2.32 KB) -- https://bugs.ruby-lang.org/ Unsubscribe: