From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2005-10-29T00:42:11+09:00
Subject: Re: Cleaner syntax for .map (is there already a way, or ruby2 idea?)

David A. Black wrote:
> Hi --
> 
> On Fri, 28 Oct 2005, Daniel Schierbeck wrote:
> 
>> David A. Black wrote:
>>
>>> Hi --
>>>
>>> On Fri, 28 Oct 2005, Daniel Schierbeck wrote:
>>>
>>>> Daniel Schierbeck wrote:
>>>>
>>>>> David A. Black wrote:
>>>>>
>>>>>> I know that people.every could return
>>>>>> some kind of generator or enumerator, which could then be fed
>>>>>> "email_addr" symbolically... 
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> module Enumerable
>>>>>   def every
>>>>>     enum, obj = self, Object.new
>>>>>     obj.define_method :method_missing do |name, *args|
>>>>>       enum.map { |element| element.send(name, *args) }
>>>
>>>
>>>
>>> If you must do this, you'd probably want each rather than map there.
>>
>>
>> Nope. I wan't it to return an array of the values returned.
> 
> 
> Oh right, never mind.
> 
>>  ["john", "sylvia", "sarah"].every.upcase -> ["JOHN", "SYLVIA", "SARAH"]
>>
>> That's of course not a very good example. This would probably be better:
>>
>>  addresses = contacts.every.email_addr
>>
>> As opposed to
>>
>>  addresses = contacts.collect { |contact| contact.email_addr }
> 
> 
> I strongly prefer the latter.  You've gone out of your way to make it
> long and wordy :-)
> 
>   addresses = contacts.map {|c| c.email_addr }
> 

That's of course a matter of taste, but I don't like single-letter 
variables. Abbreviations of long words can do, but the variable name 
should reflect the object it is referencing. Furthermore, I often use 
`collect' instead of `map' simply because that's what I'm doing: 
collecting email-addresses from a list of contacts.


>> But I agree that the dot syntax is bad, I was just proving that it 
>> could easily be done. This would be better:
>>
>>  addresses = contacts.every(:email_addr)
> 
> 
> There was an RCR once for enum.map(:method) {|x| ... } but it was
> rejected.
> 

I don't see why a method such as `map' should work that way - it isn't 
implied by the method name.

>> And maybe even have a `with_every' method:
>>
>>  contacts.with_every(:email_addr) do |email_addr|
>>    puts " - " + email_addr
>>  end
> 
> 
> "with_every" feels like the wrong word, though.  It suggests that
> they're all being used at the same time.  Maybe:
> 
>   contacts.each_send(:email_addr)
> 
> or something.
> 
> 

Maybe. `with_each' would also do. But still I think it is inconsistent 
to have `each' yield each object in a collection and `each_send` yield 
the result of calling a method on those objects. I'd rather we have 
`every' handle the latter.

   # calls `method' on each object in `collection'
   # and returns the return values of those calls
   # in an array
   collection.every :method

   # calls `method' on each object in `collection'
   # and yields the return values
   collection.with_every :method do |result|; end

They could of course both be contained in a single method, which both 
returned an array and yielded the return values.

I'm not suggesting that we put this in the Ruby Core, but I think it's a 
great library method.


Cheers,
Daniel