Array and Hash to_s

[Ben Giddings]

|#to_hash is fine by me too, but I don't really know the nuances of
|to_s/to_str, to_a/to_ary, ...

Longer versions are for implicit conversion. An object that has
"to_str" works like a string if it's given as an argument.

While we're on the subject of "to_s" and similar friends, I have a
question about Array#to_s and Hash#to_s.

I've never found them very useful the way they work by default:

irb(main):026:0> [1, 2, 3, 4].to_s
"1234"

irb(main):028:0> {1 =>2, 3 => 4}.to_s
"1234"

The main problem here is that Array#to_s calls join with the default
field separator, which for some reason is "". To me, this isn't
intuitive. Is there some historical reason why this behavior exists?
Even less intuitive to me is Hash#to_s, because the way the conversion
is done you lose any concept it was a hash.

Both of these default behaviors can be changed by setting $,

irb(main):033:0> $, = ", "
", "
irb(main):034:0> [1, 2, 3, 4].to_s
"1, 2, 3, 4"
irb(main):035:0> {1 =>2, 3 => 4}.to_s
"1, 2, 3, 4"

This is great for an array, but less great for a hash, you still lose
the key=>value association.

The main issue I have with these default to_s calls is that you seem to
lose a lot of information in the conversion. On the other hand, I
think the output from Array#inspect and Hash#inspect is great. It's
easily readable and contains all the info I want.

I'm having trouble coming up with a good example of where having a
reasonable output from some_random_object.to_s should be useful, but
how about this:

def giveRating(obj)
puts "My rating for the movie is #{obj}"
end

irb(main):049:0> giveRating("***")
My rating for the movie is: ***
nil
irb(main):050:0> giveRating("so-so")
My rating for the movie is: so-so
nil
irb(main):051:0> giveRating(7)
My rating for the movie is: 7
nil
irb(main):052:0> giveRating(["good plot", "bad writing"])
My rating for the movie is: good plotbad writing
nil
irb(main):053:0> giveRating({"acting" => 5, "music" => "awful"})
My rating for the movie is: musicawfulacting5
nil

It would be more intuitive to me if the complete default output were
something like:

irb(main):052:0> giveRating(["good plot", "bad writing"])
My rating for the movie is: good plot, bad writing
nil
irb(main):053:0> giveRating({"acting" => 5, "music" => "awful"})
My rating for the movie is: music => awful, acting => 5
nil

Any thoughts, comments, harsh criticism?

Ben

 

[Yukihiro Matsumoto]

Hi,

In message "Array and Hash to_s"

|The main issue I have with these default to_s calls is that you seem to
|lose a lot of information in the conversion. On the other hand, I
|think the output from Array#inspect and Hash#inspect is great. It's
|easily readable and contains all the info I want.

Hmm, "to_s" means "stringify", that is making a string out of an
object. It may or may not produce human readable output.

|I'm having trouble coming up with a good example of where having a
|reasonable output from some_random_object.to_s should be useful, but
|how about this:

I don't deny your desire. It is understandable. But:

* I don't think we will change "to_s" behavior for compatibility
reason. we may add a new string converter method for this
purpose.

* _you_ have to define your desire in detail; purpose, behavior, and
corner cases, to show us it's generic enough to add in the core.

Note you can add methods very easily even to the predefined classes in
Ruby.

matz.