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Feature #16987

Updated by sawa (Tsuyoshi Sawada) 3 months ago

Enumerations are designed to be greedy (immediately executed on each method call within a chain) by default. Sometimes, that is not useful for practical purposes (e.g. 2 mln strings array, drop comments, split into fields, find the first ten whose field 2 is equal to some value). So one needs to either do everything in one `each` block, or use `Enumerable#lazy`. There are three problems with the latter: 

 1. It is much less known, 
 2. It is said to be _almost always_ slower than non-lazy, and is therefore not recommended, 
 3. It lacks some methods that are often necessary in processing large data chunks. 

 I want to discuss (3) here. `Enumerator::Lazy` would better, but actually doesn't, don't, have methods such as: `#flatten`, `#product`, and `#compact`. They are all methods of the Array, not Enumerable. In fact, 
 
 1. They probably _should_ belong to `Enumerable` (none of them requires anything besides `#each` to function), 
 2. They are definitely useful for lazily processing large sequences.

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