From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2006-07-29T03:35:04+09:00
Subject: Re: Weird problem with case expressions

ara.t.howard@noaa.gov wrote:
> On Sat, 29 Jul 2006, Daniel Schierbeck wrote:
> 
>>> althogh i personally would use
>>>
>>>   [Integer, String, Array].detect{|c| c === 'foo'}
>>>
>>> since i can easily become a one liner, even with many classes.  if 
>>> you need
>>> the string then
>>>
>>>   [Integer, String, Array].detect{|c| c === 'foo' and c.name.downcase}
>>
>> That would work, but I don't think classes and types are always the 
>> same. An
>> ordered hash is still a hash, even if it doesn't descend from Hash. This
>> way, all objects that respond to #to_hash is in some way a hash, and I 
>> can
>> trust (to some degree) that the object returned when calling that method
>> implements the interface of Hash.
> 
> indeed.  still, the technique is more compact than a case:
> 
>   %w( to_int to_str to_hash to_ary ).detect{|m| 'foo'.respond_to? m}

Very nice solution! It could even be written as:

   %w{int str ary}.detect{|type| obj.respond_to? "to_#{type}"}

the only problem is that it violates DRY when used in case expressions:

   case [:int, :str, :ary].detect{|type| obj.respond_to? "to_#{type}"}
     when :int then "integer"
     when :str then "string"
     when :ary then "array"
   end

(note that this isn't about mapping "ary" to "array" -- it's about 
determining the type of an object, and behave in accordance with that.)


Cheers,
Daniel