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Q&A

Difference between puts and print for Array

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I have an array

friends = Array.new
friends[0] = "Mad man"
friends[1] = "hey"

There's two way to print them using print or, puts. At first I had tried with print

print friends

When I had run above command my output was like

["Mad man", "Hey"]

But, when I try puts. My output is ok.

puts friends

Output :

Mad man
Hey

I know that difference between puts and print is puts add a new line and, print doesn't. But, why print was directly giving output of that array (not separating them)?

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1 comment

Actually, print will add a new line if you set $\ = "\n" hkotsubo‭ 24 days ago

1 answer

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The official ruby documentation explains the observed difference between the outputs of print and puts. The important bits are as follows:


print

For any non-string object given as argument (such as an array, for example), print invokes the object's to_s method and outputs the resulting string returned by to_s. Quote from doc (link):

Each given object that isn't a string will be converted by calling its to_s method.

And as it so happens, the to_s method of your array produces the ["Mad man", "Hey"] output you observe (and which is also documented, link).


puts

On the other hand, puts behaves differently when provided with an array. Quote from doc (link):

If called with an array argument, writes each element on a new line. Each given object that isn't a string or array will be converted by calling its to_s method.

Contrary to print, puts does NOT call the array's to_s method but rather directly outputs the array elements line-by-line.


By the way, you can also achieve almost the same output as print with puts by explicitly invoking the to_s method like:

puts friends.to_s

which will output

["Mad man", "hey"]

(It is only almost the same output as print friends, since puts writes a newline at the end of the output, whereas print does not -- unless of course you change the output record separator to a newline. See also hkotsubo‭'s comment below.)

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2 comments

Actually, print will add a new line if you set $\ = "\n". The doc mentions that: "If the output record separator ($\) is not nil, it is appended to the output" - as the default value is nil, print won't normally add anything in the end (btw, you can set $\ to any string you like, and that will be added in the end). puts, on the other hand, ignores $\ and always add a newline. hkotsubo‭ 24 days ago

@hkotsubo‭ good point! elgonzo‭ 23 days ago

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