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David Eisinger
2023-10-24 20:48:09 -04:00
parent 0438a6d828
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content/elsewhere/get-lazy-with-custom-enumerators/index.md
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@@ -2,7 +2,6 @@
title: "Get Lazy with Custom Enumerators"
date: 2015-09-28T00:00:00+00:00
draft: false
needs_review: true
canonical_url: https://www.viget.com/articles/get-lazy-with-custom-enumerators/
---
@@ -32,14 +31,16 @@ related places always display, using the following logic:
Straightforward enough. An early, naïve approach:
def associated_places
[
(associated_place_1 if associated_place_1.try(:published?)),
(associated_place_2 if associated_place_2.try(:published?)),
*nearby_places,
*recently_updated_places
].compact.first(2)
end
```ruby
def associated_places
[
(associated_place_1 if associated_place_1.try(:published?)),
(associated_place_2 if associated_place_2.try(:published?)),
*nearby_places,
*recently_updated_places
].compact.first(2)
end
```
But if a place *does* have two associated places, we don't want to
perform the expensive call to `nearby_places`, and similarly, if it has
@@ -47,17 +48,19 @@ nearby places, we'd like to avoid calling `recently_updated_places`. We
also don't want to litter the method with conditional logic. This is a
perfect opportunity to build a custom enumerator:
def associated_places
Enumerator.new do |y|
y << associated_place_1 if associated_place_1.try(:published?)
y << associated_place_2 if associated_place_2.try(:published?)
nearby_places.each { |place| y << place }
recently_updated_places.each { |place| y << place }
end
end
```ruby
def associated_places
Enumerator.new do |y|
y << associated_place_1 if associated_place_1.try(:published?)
y << associated_place_2 if associated_place_2.try(:published?)
nearby_places.each { |place| y << place }
recently_updated_places.each { |place| y << place }
end
end
```
`Enumerator.new` takes a block with "yielder" argument. We call the
yielder's `yield` method[^1^](#fn:1 "see footnote"){#fnref:1 .footnote},
yielder's `yield` method[^1],
aliased as `<<`, to return the next enumerable value. Now, we can just
say `@place.associated_places.take(2)` and we'll always get back two
places with minimum effort.
@@ -70,9 +73,4 @@ by Pat Shaughnessy and [*Lazy
Refactoring*](https://robots.thoughtbot.com/lazy-refactoring) on the
Thoughtbot blog.
\* \* \*
1. ::: {#fn:1}
Confusing name -- not the same as the `yield` keyword.
[ ↩](#fnref:1 "return to article"){.reversefootnote}
:::
[^1]: Confusing name -- not the same as the `yield` keyword.