Question

In my script (for Ruby >= 1.9) below I defined a Table class, which responsability is to generate 2 to 10 addition or multiplication table (chosen with a parameter). Then I call table method from a new Table instance in order to print result in a file.

This is the script :

#!/usr/bin/env ruby

class Table

HEADER_LINE = "="*25
add_operation = lambda { |op1, op2| op1 + op2 }
mul_operation = lambda { |op1, op2| op1 * op2 }

def table(req_operation = :mul)

    operation, op_label =   case req_operation
                            when :add
                                [add_operation, "+"]
                            when :mul
                                [mul_operation, "*"]
                            else
                                raise "Unknown operation #{req_operation} !"
                            end


    (2..10).each do |op1|
        yield HEADER_LINE
        yield "Table de #{op1} (x#{op_label}y)"
        yield HEADER_LINE
        (1..10).each do |op2|
            yield line = "#{op1} #{op_label} #{op2} = #{operation.call(op1, op2)}"
        end
        yield HEADER_LINE
        yield
    end
end

end

File.open("MyFile", "w") do |file|
    Table.new.table do |line|
        file.write "#{line}\n"
    end
end

The parallel assignement on line 11 tries to set a lambda to operation and a string to op_label. Indeed, on line 26, I want to apply the lambda to op1 and op2 local variables.

But I get the following error :

./operation_table.rb:15:in `table': undefined local variable or method `mul_operation' for #<Table:0x00000000f1fc48> (NameError)
    from ./operation_table.rb:38:in `block in <main>'
    from ./operation_table.rb:37:in `open'
    from ./operation_table.rb:37:in `<main>'

Is there a way to correct it while keeping the parallel assignement ?
Thanks in advance.

Answer 1

add_operation and mul_operation are local variables, declared outside the function, and cannot be accessed by the function table.

You can declare it inside the table function, or store as class variables.

def table(...)
  add_operation = lambda { |op1, op2| op1 + op2 }
  mul_operation = lambda { |op1, op2| op1 * op2 }
  ...
end