From: Guido De Rosa <guidoderosa@...>
Date: 2010-10-07T20:32:54+09:00
Subject: Re: "map" a deeply nested structure: Object#deep_map

Robert Klemme wrote:

> Guido De Rosa wrote:
>>
>> Of course it depends by the usage scenario, and I actually found such a
>> need in one of my production projects. I may tell you longer detail if
>> you wish...
> 
> Yes, please.
> 
>> Of course there's no need that the values belong to the same class or to
>> derived class, they just need to be uniform in the duck-typing sense.
>>
>> Consider something like:
>>
>>    my_deep_structure.deep_map{|v| v.to_s}
> 
> What do you need that for?  If it is for printing or logging then you
> can use my_deep_structure.to_s or my_deep_structure.inspect.
> 
>> this more convenient that overwriting to_json, to_yaml, marshal_dump and
>> so on...
> 
> You really make me curious about your use case.

This is embarrassing but I'm thinking - right now - that I made some 
other mistakes in "my use case". Thanks for the head-ups, this 
discussion has proven useful.

What I will do, if you're still curious, is just provide a link to my 
fixes (as git commits, when they are done).

Now, don't mind my use case. Let's return to my first post.

My conclusion is that the method I wrote should be renamed 
deep_map_values. And another method may be called deep_rekey with 
obvious behavior.

Hash#map is totally another beast:

  1. it mixes key and values in the transformation (which may lead to
     unwanted results in a hypothetical recursive version IMHO)

  2. it turns an Hash into an Array of pairs (which may be what you
     want, or not)

Regards,
Guido
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