Feature #13290: A method to use a hash like in a case construction

• Status: Feedback
• Assignee: -
• Target version: -

[sawa (Tsuyoshi Sawada)]

We often want to translate a hash into a case construction and back. For example, suppose we have a case construction like this:

case key
when /foo/ then "FOO"
when /bar/ then "BAR"
else "DEFAULT"
end

Given that the keys are ordered within a hash since Ruby 1.9, the information used in the case construction above can be expressed as a hash h:

h = {
  /foo/ => "FOO"
  /bar/ => "BAR"
  ...
}
h.default = "DEFAULT"

At the moment, there is no straightforward way to translate the hash h into the case construction as above. I would like to have a method on Hash that takes a key and works like a case construction (i.e., applies the === method) as below:

h.fetch_as_in_case_construction("barbar") # => "BAR"

The name fetch_as_in_case_construction is terrible. Perhaps someone can suggest a better name.

[shevegen (Robert A. Heiler)]

I love case/when menus, so I am all for suggestions that make case/when more
useful, so I also support this (even if this one is indirect, on class Hash,
to have them behave like a case/when menu).

I also would like to see case/when become first-class citizens (objects) one day
that can also be merged together (e. g. unify two different case/when menus
together, both working on the same variable... a bit similar as to how hashes
can be merged together too. A bit like UnboundMethod where we could, in
theory, detach a method and attach it to another object or use another
environment ... but I digress again, sorry.)

The name "fetch_as_in_case_construction" is indeed a bit terrible,
I am glad that I am not the only one who suggests terrible names. :D

But I think the more important part is whether matz/ruby core team
think that the underlying functionality would be ok to be had.

Finding good names is hard but possible! I also have no really better
suggestion. My suggestions may even be worse ... such as :)

Obvious ones would be ".to_case" or, if the other way around, on
a first-class citizen case object, .to_hash. Or some method called
"convert" or "transform" or "treat_as_case" or ... I dunno.

But +1 anyway.

[duerst (Martin Dürst)]

Tsuyoshi Sawada wrote:

The name fetch_as_in_case_construction is terrible. Perhaps someone can suggest a better name.

What about simplifying this to fetch_as_case? Or maybe even just case? Just thinking out loud.

[mame (Yusuke Endoh)]

h.find {|a,| a === "barbar" }.last #=> "BAR"

This is good enough to me.

[sawa (Tsuyoshi Sawada)]

Yusuke Endoh wrote:

h.find {|a,| a === "barbar" }.last #=> "BAR"

This is good enough to me.

I expected something that would be as easy as and comparable to h[key].

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Feedback

I don't see how mush useful this proposal is. Please show us concrete use-case.

Matz.