More on the fundamentals

ruby-talk
1

Please have a look at the comments below to see that I'm understanding things correctly;

#!/usr/bin/ruby
#Tue Jan 3 14:04:28 GMT 2006
class Greeter
        # a new class cllaed Greeter
        def initialize(name)
                # creating a new method called name
                @name = name
                # we define a new @instance variable called name
        end
        def say(phrase)
                # creating a new method called phrase...
                puts "#{phrase}, #{@name}"
                # ... which uses doube quotes to substitute
        end
end

# say hello
g1 = Greeter.new("jayeola")
g2 = Greeter.new("buddy")
g3 = Greeter.new("vimmer")
g4 = Greeter.new("slammer")
# we have just created four new (object) instances belonging to the class
# Greeter. They can now use the instance variables that have been created
# above
g1.say("Hello")
g2.say("Wotcha")
g3.say("Ire!")
g4.say("Elake")

···

--
John Maclean
MSc (DIC)
07739 171 531

2

Hi --

Please have a look at the comments below to see that I'm
understanding things correctly;

#!/usr/bin/ruby
#Tue Jan 3 14:04:28 GMT 2006
class Greeter
       # a new class cllaed Greeter
       def initialize(name)
               # creating a new method called name

There's no method called name.

               @name = name
               # we define a new @instance variable called name

Move the @ from @instance to name and you're set :slight_smile:

       end
       def say(phrase)
               # creating a new method called phrase...

There's no method called phrase.

               puts "#{phrase}, #{@name}"
               # ... which uses doube quotes to substitute
       end
end

It seems that you're confusing instance variable assignment with
method creation. They're unrelated. You can, of course, write a
method that returns the current value of an instance variable:

   def name
     @name
   end

and you can even get Ruby to do it semi-automatically for you:

   attr_reader :name # creates the above "name" method

But @name = name is just a variable assignment.

# say hello
g1 = Greeter.new("jayeola")
g2 = Greeter.new("buddy")
g3 = Greeter.new("vimmer")
g4 = Greeter.new("slammer")
# we have just created four new (object) instances belonging to the class
# Greeter. They can now use the instance variables that have been created

I would say "instances of the class Greeter".

# above
g1.say("Hello")
g2.say("Wotcha")
g3.say("Ire!")
g4.say("Elake")

Have another look at the attr_* family of methods, and keep in mind
that they're essentially shortcuts for writing your own get-and/or-set
methods (using instance variables), and I think that part of it will
fall into place.

David

···

On Tue, 3 Jan 2006, John Maclean wrote:

--
David A. Black
dblack@wobblini.net

"Ruby for Rails", from Manning Publications, coming April 2006!

3

Please have a look at the comments below to see that I'm understanding things correctly;

You've made a couple of fundamental mistakes regarding how methods are defined. The basic schema is:

def method_name(parameter_name)

Where you can have a whole list of parameters, or none at all. See the revised (and very verbose comments. Hope this helps.

matt smillie.

Also, I've changed the indented to two spaces, since that's the Ruby norm.

class Greeter
   # open class Greeter (it's not necessarily *new*)
   def initialize(name)
     # defining the initialise method, which is called when a new
     # object is created. The method takes one parameter, 'name'.
     # Example (such as: foo = Greeter.new("Mark").
     @name = name
     # define an instance variable called '@name' and assign it
     # the value of the parameter 'name'
   end

   def say(phrase)
     # defining a new method called 'say' with a parameter
     # called 'phrase'.
     puts "#{phrase}, #{@name}"
     # The double quotes define a string, and the #{} sections are
     # used for interpolation (substitution).
   end
end

···

On Jan 3, 2006, at 14:51, John Maclean wrote:

#!/usr/bin/ruby
#Tue Jan 3 14:04:28 GMT 2006
class Greeter
        # a new class cllaed Greeter
        def initialize(name)
                # creating a new method called name
                @name = name
                # we define a new @instance variable called name
        end
        def say(phrase)
                # creating a new method called phrase...
                puts "#{phrase}, #{@name}"
                # ... which uses doube quotes to substitute
        end
end

# say hello
g1 = Greeter.new("jayeola")
g2 = Greeter.new("buddy")
g3 = Greeter.new("vimmer")
g4 = Greeter.new("slammer")
# we have just created four new (object) instances belonging to the class
# Greeter. They can now use the instance variables that have been created
# above
g1.say("Hello")
g2.say("Wotcha")
g3.say("Ire!")
g4.say("Elake")

--
John Maclean
MSc (DIC)
07739 171 531

4

In this line of code can anyone tell me why "food" is a method? I thought that they are preceded by a dot.

    __ an array __ the method __ parameters for code block
   / / /
  [cornflakes, yam, rice].each { |food| eat food}
                               / \
              code block __/ \__block args

···

On Tue, 3 Jan 2006 23:51:15 +0900 John Maclean <info@jayeola.org> wrote:

Please have a look at the comments below to see that I'm understanding things correctly;

#!/usr/bin/ruby
#Tue Jan 3 14:04:28 GMT 2006
class Greeter
        # a new class cllaed Greeter
        def initialize(name)
                # creating a new method called name
                @name = name
                # we define a new @instance variable called name
        end
        def say(phrase)
                # creating a new method called phrase...
                puts "#{phrase}, #{@name}"
                # ... which uses doube quotes to substitute
        end
end

# say hello
g1 = Greeter.new("jayeola")
g2 = Greeter.new("buddy")
g3 = Greeter.new("vimmer")
g4 = Greeter.new("slammer")
# we have just created four new (object) instances belonging to the class
# Greeter. They can now use the instance variables that have been created
# above
g1.say("Hello")
g2.say("Wotcha")
g3.say("Ire!")
g4.say("Elake")

--
John Maclean
MSc (DIC)
07739 171 531

5

John Maclean <info@jayeola.org> writes:

In this line of code can anyone tell me why "food" is a method? I
thought that they are preceded by a dot.

It is not a method, it's a variable, very possibly a block-local one.

    __ an array __ the method __ parameters for code block
   / / /
  [cornflakes, yam, rice].each { |food| eat food}
                               / \
              code block __/ \__block args

^^^ is parsed as: [corflakes, yam, rice].each {|food| eat(food)}

YS.

···

On Tue, 3 Jan 2006 23:51:15 +0900 > John Maclean <info@jayeola.org> wrote:

Please have a look at the comments below to see that I'm understanding things correctly;

#!/usr/bin/ruby
#Tue Jan 3 14:04:28 GMT 2006
class Greeter
        # a new class cllaed Greeter
        def initialize(name)
                # creating a new method called name
                @name = name
                # we define a new @instance variable called name
        end
        def say(phrase)
                # creating a new method called phrase...
                puts "#{phrase}, #{@name}"
                # ... which uses doube quotes to substitute
        end
end

# say hello
g1 = Greeter.new("jayeola")
g2 = Greeter.new("buddy")
g3 = Greeter.new("vimmer")
g4 = Greeter.new("slammer")
# we have just created four new (object) instances belonging to the class
# Greeter. They can now use the instance variables that have been created
# above
g1.say("Hello")
g2.say("Wotcha")
g3.say("Ire!")
g4.say("Elake")

--
John Maclean
MSc (DIC)
07739 171 531

6

Quoting John Maclean <info@jayeola.org>:

In this line of code can anyone tell me why "food" is a method? I
thought that they are preceded by a dot.

    __ an array __ the method __ parameters for code
block
   / / /
  [cornflakes, yam, rice].each { |food| eat food}
                               / \
              code block __/ \__block args

Within the context of the block, "food" is a variable. "eat",
however, will be interpreted as a private method call (i.e. as a
call to the "eat" method on self), provided an "eat" variable does
not already exist in that scope.

Generally, given a bare identifier, the rule is:

1. If a previous assignment to the name exists in the current scope
(whether or not it was actually performed), the name is a variable
(or a parse error if you try to give it parameters)

2. otherwise, it is a call to a private method on self

Examples:

1. foo # method

2. foo = 1
    foo # variable

3. if false
      foo = 1 # never executed
    end
    foo # still a variable (initialized to nil)

4. [1, 2, 3].each { |foo| # introduced as block param
      foo # variable here
    }
    foo # method call here

5. foo = 1
    foo # variable
    [1, 2, 3].each { |foo| # same variable
      foo # yes, same variable
    }
    foo # still same variable

-mental