What Are <-- Ruby Strings Called? and How to Insert Variables in Them

What are -- Ruby Strings called? And how do I insert variables in them?

That syntax is for declaring a HERE DOCUMENT
http://www.ruby-doc.org/docs/ruby-doc-bundle/Manual/man-1.4/syntax.html#here_doc

There's a line-oriented form of the string literals that is usually
called as `here document'. Following a << you can specify a string or
an identifier to terminate the string literal, and all lines following
the current line up to the terminator are the value of the string. If
the terminator is quoted, the type of quotes determines the type of
the line-oriented string literal. Notice there must be no space
between << and the terminator.

If the - placed before the delimiter, then all leading whitespcae
characters (tabs or spaces) are stripped from input lines and the line
containing delimiter. This allows here-documents within scripts to be
indented in a natural fashion.

Regarding interpolation, the link gives more details, but it is like a double quoted string if your string is delimited as below (ignore this page's color formatting)

<<-HERE
   I can interpolate #{foo}
HERE

whereas it is like a single quoted string

<<-'HERE'
 This will print out #{foo} as text
HERE

Also the original pickaxe is a good source http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html

Ruby: Merging variables in to a string

The idiomatic way is to write something like this:

"The #{animal} #{action} the #{second_animal}"

Note the double quotes (") surrounding the string: this is the trigger for Ruby to use its built-in placeholder substitution. You cannot replace them with single quotes (') or the string will be kept as is.

Ruby strings with embedded variables

str = "Hi %{name}, %{msg}. Bye %{name}." #yaml it, de-yaml it back to string
h = {:name=> "John", :msg=> "this message is for you"}
puts str % h
#=>Hi John, This message is for you. Bye John.

How to insert variable into formatted text in ruby

Just use uppercase "Q"

variable = "some string"
%Q{ My math #{1+1} and string #{variable}}

Ruby -- use a string as a variable name to define a new variable

There is no way to define new local variables dynamically in Ruby.

It was possible in Ruby 1.8 though with eval 'x = 2'.

You can change an existing variable with eval or binding.local_variable_set.

I would consider using hash to store values.

How to create and use variables dynamically named by string values in Ruby?

Instance variables are used define properties of an object.

Instead you can achieve through the method send and string interpolation.

Try the below:

def click_colour_cell(colour)
  send("has_#{colour}_colour_cell?")
  send("#{colour}_colour_cell").click
end

About Send:

send is the method defined in the Object class (parent class for all the classes).

As the documentation says, it invokes the method identified by the given String or Symbol. You can also pass arguments to the methods you are trying to invoke.

On the below snippet, send will search for a method named testing and invokes it.

class SendTest
  def testing
    puts 'Hey there!'
  end
end


obj = SendTest.new
obj.send("testing")
obj.send(:testing)

OUTPUT

Hey there!
Hey there!

In your case, Consider the argument passed for colour is blue,

"has_#{colour}_colour_cell?" will return the string"has_blue_colour_cell?" and send will dynamically invoke the method named has_blue_colour_cell?. Same is the case for method blue_colour_cell

Is it possible to insert one variable's value into the name of another variable?

Yes, you can do do this:

if @count < 1001
  instance_variable_set("@#{@count}", @count + 1)
end

It would be more idiomatic to store in a hash, e.g.

h = {}
if @count < 1001
  h[@count] = @count + 1
end

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