Re: wondering about #tap

Hi --

On Sat, 17 Nov 2007, David Flanagan wrote:

> David A. Black wrote:
>> Hi --
>> 
>> On Fri, 16 Nov 2007, Michael Neumann wrote:
>> 
>>> If you use Ruby 1.9, you can use Object#tap:
>>>
>>>  "I am a 20MB string".tap {|i| i.downcase!}.split(/\s+/).tap {|i|
>>>  i.reject!{|s|s.length>20}
>>> 
>>> But why not split it in multiple lines? I think it will become more 
>>> readable than using #tap:
>>>
>>>  str = "..."
>>>  str.downcase!
>>>  arr = str.split(..)
>>>  arr.reject!{...}
>> 
>> It's interesting that almost every example of #tap ends up saying that
>> it's probably better not to use it, for one reason or another (usually
>> readability; sometimes the dangers of mixing bang and non-bang
>> methods).
>> 
>> It makes me wonder whether the main effect of #tap is going to be a
>> lot of warnings that it isn't a best practice. Or are there examples
>> that *don't* look worse than the alternatives?
>> 
>> 
>> David
>> 
>
> The use case that occurs to me (I'm not sure that it will convince you 
> though) is to "tap" into an already existing method chain.  The existence of 
> tap shouldn't cause the creation of longer chains, but if someone is writing 
> in that style, it is nice to be able to insert things, like debugging or 
> logging output, without breaking the chain up.
>
> Here's the (extreme) example from my book:
>
> chars = "hello world".tap {|x| puts "original object: #{x.inspect}"}
>  .each_char         .tap {|x| puts "each_char returns: #{x.inspect}"}
>  .to_a              .tap {|x| puts "to_a returns: #{x.inspect}"}
>  .map {|c| c.succ } .tap {|x| puts "map returns: #{x.inspect}" }
>  .sort              .tap {|x| puts "sort returns: #{x.inspect}"}
>
> The method chain goes vertically down the page, relying the new 
> fluent-programming syntax Matz enabled, and the taps stretch out 
> horizontally.

I wouldn't use the term "fluent" to describe this new and, to my eye,
very jarring idiom. It seems significantly *less* fluent -- meaning,
it doesn't flow; you have to backtrack to the previous line to figure
out what the line with the dot is doing. I'm rooting for it to be
backed out of 1.9, or at least 2.0.

The tap example, as a kind of debugging apparatus, is interesting and
looks like it could have its uses. I'm not sure it's worth risking all
the ugliness, but maybe :-)


David

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