Don't understand Ruby ljust/rjust/center methods - ruby

Question

I'm learning the nesting and my task is to make each new line start with an indent. Here's my code, but it doesn't work
$nestingDepth = 0
def logger description, &block
puts "Beginning #{description}".rjust($nestingDepth)
puts $nestingDepth
$nestingDepth = $nestingDepth + 10
result = block.call
$nestingDepth = $nestingDepth - 10
puts $nestingDepth
puts "End of #{description} block that returned #{result}".rjust($nestingDepth)
end
logger "first block" do
logger "second block" do
logger "third block" do
puts "third block part"
end
puts "second block part"
end
puts "first block part"
end

Answer 1

Your code has several problems:
you are using global variables which is generally a bad idea, pass it down as an argument instead. To do this you can use a DSL class that defines the logger and log methods.
you are calling puts inside the blocks, but you never changed the definition of it, I don't see how you were expecting it to print an indented string, it will just print the string normally without indentation. For this to work you need to define a special method that prints with indentation, e.g. log
you are calling rjust with the expectation that it will indent the string. This method has a different purpose - justifying a string to the right (i.e. left-padding it) with a specified length. If the string is longer than the specified length, the original string is returned. To actually indent a string you should do puts ' ' * nestingDepth + string. Looks magic at first, but the * operator just repeats the string, e.g. 'abc' * 3 #=> 'abcabcabc'
All taken together I would do it like this:
class DSL
def initialize
#depth = 0
end
def logger(description, &block)
log "Beginning #{description}"
#depth += 1
result = instance_eval(&block)
#depth -= 1
log "End of #{description} that returned #{result}"
end
def log(string)
puts indent + string
end
private
def indent
' ' * (10 * #depth)
end
end
def logger(*args, &block)
DSL.new.logger(*args, &block)
end
Example:
logger "first block" do
logger "second block" do
logger "third block" do
log "third block part"
end
log "second block part"
end
log "first block part"
end
This prints:
Beginning first block
Beginning second block
Beginning third block
third block part
End of third block that returned
second block part
End of second block that returned
first block part
End of first block that returned

Answer 2

Your issue is that rjust requires an integer greater than the length of the string it's applied on. Your string is:
"Beginning #{description}"
Which turns into:
Beginning first block
Beginning second block
On most passes this is either a length of 21 or 22. The largest you ever make $nestingdepth is 20. When the integer is less than the length of the string it just returns the string with no padding. If I start the script with a nesting depth of 25 you see it unfold.
Beginning first block
25
Beginning second block
35
Beginning third block
45