From: eregontp@... Date: 2019-06-06T09:36:15+00:00 Subject: [ruby-core:93005] [Ruby trunk Feature#15901] Enumerator::Lazy#eager Issue #15901 has been updated by Eregon (Benoit Daloze). knu (Akinori MUSHA) wrote: > Suppose I want to pass the `enum` to another method that takes an Enumerable object where the passed object is expected to act eagerly. One of the most significant use cases is when the callee uses `take_while` on a given object expecting to receive the result as an array, where a normal Enumerable object that generates a list lazily is ideal. I see, thanks for explaining. One argument would be the callee should do `take_while {}.to_a` if they really want an `Array` and not just an `Enumerable` (which has most of `Array`'s methods). But I understand it's nice to be able to use an unmodified library and not needing the library to know about Enumerator::Lazy. ---------------------------------------- Feature #15901: Enumerator::Lazy#eager https://bugs.ruby-lang.org/issues/15901#change-78382 * Author: knu (Akinori MUSHA) * Status: Open * Priority: Normal * Assignee: * 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: