Noob question re:returning nil

Ruby
1

Hello all, I am a beginner programmer and a beginner to Ruby. I was just
going through a tutorial book and trying to create some programs. The
current program I am working on I am having trouble with.

I have defined a method and the last thing in the method is a puts
concatenation. The program runs and does everything correctly except for
when I call the method it puts the string and then nil underneath.

I thought the return value was the last value of the string so I don’t
understand why it is doing this. How do I get rid of the nil?

2

On 2011-04-13, at 21:27, Nathan McDorman wrote:

Hello all, I am a beginner programmer and a beginner to Ruby. I was just
going through a tutorial book and trying to create some programs. The
current program I am working on I am having trouble with.

I have defined a method and the last thing in the method is a puts
concatenation. The program runs and does everything correctly except for
when I call the method it puts the string and then nil underneath.

I thought the return value was the last value of the string so I don’t
understand why it is doing this. How do I get rid of the nil?

If I’m not mistaken, you’re doing something like this.

irb(main):001:0> def myputs(x)
irb(main):002:1> puts("" + x + "")
irb(main):003:1> end
=> nil
irb(main):004:0> myputs(“foobar”)
foobar
=> nil

The return value of myputs is the value of the last expression, which is
whatever puts returns. If you do ri ‘Kernel#puts’, you will find that it
always returns nil, which is what you’re getting. That’s a
characteristic of Kernel#puts. The other piece to the puzzle is that irb
displays the return value of whatever you enter. So calling myputs
displays a message, and then shows the return value of nil.

There may be a way of turning off the display of returned values in irb.
If so, I don’t know what it is, because I’ve never wanted to use it.
Maybe someone else can tell you that.

The important point is that displaying the returned value is only a
characteristic of irb. Running a program via the ruby command doesn’t
display return values, and therefore you only get printed that which you
explicitly specify is to be printed, via puts or print or some such.

Hope that helps – vincent

3

Thank you guys so much I really appreciate the help! I’ve changed the
program to a method that just calculates what I want it to return and
holds it in a var placed at the end of the method. Then I call puts
outside of the method on the method.

4

On Thu, Apr 14, 2011 at 01:27:48PM +0900, Nathan McDorman wrote:

Hello all, I am a beginner programmer and a beginner to Ruby. I was just
going through a tutorial book and trying to create some programs. The
current program I am working on I am having trouble with.

I have defined a method and the last thing in the method is a puts
concatenation. The program runs and does everything correctly except for
when I call the method it puts the string and then nil underneath.

I thought the return value was the last value of the string so I don’t
understand why it is doing this. How do I get rid of the nil?

Evaluating puts returns nil. If you want to have a puts in the
method, then return the value of the string, you’ll have to do something
to return the value of the string explicitly after the puts
expression.

For instance, this will return nil:

def foo
  puts 'one' + ' ' + 'two'
end

This will return 'one two':

def foo
  puts (bar = 'one' + ' ' + 'two')
  bar
end

On the other hand, you’re probably better off saving your puts for the
output of the method, unless the puts is the only reason to have the
method. For instance, this:

def concat(foo,bar)
  foo + ' ' + bar
end

puts combined = concat('one','two')

. . . is probably better than this:

def concat(foo,bar)
  puts combined_val = foo + ' ' + bar
  combined_val
end

combined = concat('one', 'two')

The reason it’s probably better is that the second example does things
inside the method that is not actually part of the core reason for the
method, and you actually save complexity by handling the output method
puts outside of the method.

I hope that helps.

5

On Thu, Apr 14, 2011 at 02:55:30PM +0900, Nathan McDorman wrote:

Thank you guys so much I really appreciate the help! I’ve changed the
program to a method that just calculates what I want it to return and
holds it in a var placed at the end of the method. Then I call puts
outside of the method on the method.

I’m glad we were able to help.

Enjoy!