with and without Song#to_s again

[chen li]

Hi all,

I posted a similar question a short time ago. But I
don't think the replies help me understand the
behaviors. So I post a short version( sorry if it
bothers you again).

I have the following script. I don't call Song#to_s in
my script but I can print all the attributes of a
song. Why is that?

Thanks,

Li

#########
class Song
def initialize(name,artist,duration)
@name=name
@artist=artist
@duration=duration
end
#attr_reader :name, :artist, :duration

def to_s
"#@name\t#@artist\t\t#@duration"
end
end


s=Song.new('song1','author1','20')
puts s

######output

ruby ruby20c.rb song1 author1 20
Exit code: 0

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[Vincent Fourmond]

#########
class Song
def initialize(name,artist,duration)
@name=name
@artist=artist
@duration=duration
end
#attr_reader :name, :artist, :duration

def to_s
"#@name\t#@artist\t\t#@duration"
end
end


s=Song.new('song1','author1','20')
puts s

######output

As s is not a String (that is not s.is_a? String), it is converted
into string by puts. That exactly means your method to_s is called for
doing so.

Vince

 

[Phrogz]

I have the following script. I don't call Song#to_s in
my script but I can print all the attributes of a
song. Why is that?

chen li, you can find this answer yourself.
1) Open a console and type:
ri Kernel.puts

2) See that it says that it's the same as $stdout.puts. Type:
ri IO.puts

3) See that it says that it does the same thing as print does. Type:
ri IO.print

4) See that it tells you that it calls the to_s method of any objects
that aren't strings.