From: eregontp@... Date: 2019-06-06T17:00:20+00:00 Subject: [ruby-core:93012] [Ruby trunk Feature#15901] Enumerator::Lazy#eager Issue #15901 has been updated by Eregon (Benoit Daloze). knu (Akinori MUSHA) wrote: > > 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. > > Yeah, that would be the way completely against duck-typing. Right, to clarify I meant the library would need the extra `.to_a` where it expects an Enumerator method to return an Array and not just some `Enumerable`. So basically it would need to know that a Enumerator::Lazy could be passed, and so the extra `.to_a` is needed. If the library treat the result just like an Enumerable, no modification would be needed. Anyway, :+1: from me. ---------------------------------------- Feature #15901: Enumerator::Lazy#eager https://bugs.ruby-lang.org/issues/15901#change-78388 * 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: