From: zverok.offline@gmail.com
To: ruby-core@ruby-lang.org
Subject: [ruby-core:95117] [Ruby master Feature#16183] Hash#with_default
Date: Thu, 26 Sep 2019 19:23:41 +0000 (UTC) [thread overview]
Message-ID: <redmine.journal-81751.20190926192341.35b54382508b5664@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-16183.20190926130122@ruby-lang.org
Issue #16183 has been updated by zverok (Victor Shepelev).
> Duplicate of #11761
I don't think it is a duplicate, though I haven't clarified an important behavior indeed:
```ruby
h = {a: 1, b: 2}
h2 = h.with_default(3)
h.default # => nil
h2.default # => 3
```
So, I propose side-effect-less method, that **is** acceptable for chaining, I believe.
----------------------------------------
Feature #16183: Hash#with_default
https://bugs.ruby-lang.org/issues/16183#change-81751
* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
* Assignee:
* Target version:
----------------------------------------
Reasons: there is no way, currently, to *declaratively* define Hash with default value (for example, to store it in constant, or use in an expression). Which leads to code more or less like this:
```ruby
FONTS = {
title: 'Arial',
body: 'Times New Roman',
blockquote: 'Tahoma'
}.tap { |h| h.default = 'Courier' }.freeze
# Grouping indexes:
ary.each_with_object(Hash.new { |h, k| h[k] = [] }).with_index { |(el, h), idx| h[el.downcase] << idx }
```
With proposed method:
```ruby
FONTS = {
title: 'Arial',
body: 'Times New Roman',
blockquote: 'Tahoma'
}.with_default('Courier').freeze
ary.each_with_object({}.with_default { [] }).with_index { |(el, h), idx| h[el.downcase] << idx }
```
About the block synopsys: I am not 100% sure, but I believe that _most_ of the time when `default_proc` provided, it looks like `{ |h, k| h[k] = some_calculation }`. So, I believe for this "declarative simplification" of defaults, it is acceptable to assume it as the only behavior (pass only key to block, and always store block's result); more flexible form would still be accessible with `Hash.new`.
--
https://bugs.ruby-lang.org/
next prev parent reply other threads:[~2019-09-26 19:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <redmine.issue-16183.20190926130122@ruby-lang.org>
2019-09-26 13:01 ` [ruby-core:95104] [Ruby master Feature#16183] Hash#with_default zverok.offline
2019-09-26 15:52 ` [ruby-core:95114] " sawadatsuyoshi
2019-09-26 16:36 ` [ruby-core:95115] " shevegen
2019-09-26 19:23 ` zverok.offline [this message]
2019-09-26 21:49 ` [ruby-core:95120] " eregontp
2019-09-27 6:02 ` [ruby-core:95125] " zverok.offline
2019-09-27 8:35 ` [ruby-core:95127] " duerst
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