Feature #10064
closed
&:symbol in when clause
Description
Now we can put Proc objects in a when clause as this code.
require 'prime' def test(n) print "#{n} is " case n when :zero?.to_proc puts 'zero' when :even?.to_proc puts 'an even number' when :prime?.to_proc puts 'a prime number' else puts 'a non-prime odd number' end end (1..10).each &method(:test) I would like to write it as below:
require 'prime' def test(n) print "#{n} is " case n when &:zero? puts 'zero' when &:even? puts 'an even number' when &:prime? puts 'a prime number' else puts 'a non-prime odd number' end end (1..10).each &method(:test) How do you think about this new syntax, Matz?
Updated by ko1 (Koichi Sasada) over 11 years ago
just idea.
class Symbol def ~@ self.to_proc end end case 0 when ~:zero? p :zero end 
Updated by matz (Yukihiro Matsumoto) over 11 years ago
- Status changed from Open to Feedback
The original idea includes dispatch based on type (Symbol), which is not a good idea in general.
The one proposed by ko1 is slightly better, yet I still don't love it.
Matz.
Updated by sawa (Tsuyoshi Sawada) about 11 years ago
What about allowing syntax like this:
->&Proc.new{|y| y.zero?} #=> Should be equivalent to ->{|x| x.zero?} ->&:zero? #=> Should be equivalent to ->{|x| x.zero?} (Symbol#to_proc applies implicitly) This would be a parallel to
[*["foo"]] #=> ["foo"] [*{foo: "bar"}] #=> [[:foo, "bar"]] (Symbol#to_a applies implicitly) under the understanding that what [] is to * (converse operation) is what -> is to &.
Then, we would be able to do:
case 0 when ->&:zero? p :zero end 
Updated by marcandre (Marc-Andre Lafortune) about 11 years ago
Yukihiro Matsumoto wrote:
The original idea includes dispatch based on type (Symbol), which is not a good idea in general.
I'm not sure I understand. I think the original idea would work for other types too; the syntax would just be a shortcut for a call to to_proc.
For example, I'd expect the following to work too:
x = Object.new def x.to_proc -> { true } end case 42 when &x puts "Always true" end 
Updated by naruse (Yui NARUSE) almost 8 years ago
- Target version deleted (
2.2.0)