Issue #5553 has been updated by Alexey M…
I see. But then you may also want to pass a second procedure which is
run if the key does not exist, and to have both the key and the value
passed to the procedures, that is to introduce a method of the form
#fetch_and_use(key, proc_if_key_found, proc_if_not), but this will cost
having to store the procedures in variables for a one-time use. Also I
am afraid that optimizing like this for all possible use cases may
require introducing many new methods.
On the other hand, if you want to use a hash in this way with same
procedures multiple times, then what about adding a method
Hash#on_found_proc= analogous to Hash#default_proc= to be able to
do like this:
a = {morning: “おはよう”, daytime: “こんにちは”, evening: “こんばんは”, nothing: nil}
a.default = “どうも”
a.on_found_proc = proc do |hash,key,value|
“#{value}世界!”
end
a[:morning] # => “おはよう世界!”
a[:night] # => “どうも”
Feature #5553: A method for Hash that works differently depending on
whether a key exists
http://redmine.ruby-lang.org/issues/5553
Author: Tsuyoshi Sawada
Status: Feedback
Priority: Normal
Assignee:
Category:
Target version:
A method Hash#if_key(key, [default], &pr) which works like the following
will be often used, and is useful.
a = {morning: "おはよう", daytime: "こんにちは", evening: "こんばんは", nothing:
nil}
a.if_key(:morning){|str| “#{str}世界!”} #=> “おはよう世界!”
a.if_key(:nothing){|str| “#{str}世界!”} #=> “世界!”
a.if_key(:midnight){|str| “#{str}世界!”} #=> nil
a.if_key(:nothing, “どうも”){|str| “#{str}世界!”} #=> “どうも”
That is, when key' exists, then the corresponding value will be passed topr’. Otherwise, the given `default’ or the implicit default will be
returned.