From: ruby-core@... Date: 2019-06-13T22:03:54+00:00 Subject: [ruby-core:93117] [Ruby trunk Feature#15901] Enumerator::Lazy#eager Issue #15901 has been updated by marcandre (Marc-Andre Lafortune). zverok (Victor Shepelev) wrote: > > How about this style? > > ```ruby > [0, 1, 2].lazy {|e| e.map {|n| n + 1 }.map {|n| n.to_s } } > #=> an Enumerator containing "1", "2", and "3" > ``` > > I believe that it defies the whole idea of lazy enumerators. instead of lazy enums being "just enums", it requires wrapping everything I don't see how the suggestion defies anything, changes the current `lazy` method (without block) and or "requires" anything. It simply extends it with a block form that would automatically return an eager enumerator. My issue with `lazy{}` is that it forces the user to return a lazy enumerator from the block (otherwise it raises?, e.g. `[1].lazy{ 42 } # => RuntimeError?`). The fact that the result could be completely unrelated is for me a design smell, e.g. `[1].lazy { [1, 2, 3].lazy }`. I'm personally +1 for `eager`. I'd also alias `Enumerator#eager` to `#itself`. ---------------------------------------- Feature #15901: Enumerator::Lazy#eager https://bugs.ruby-lang.org/issues/15901#change-78543 * 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: