Method: ConvertableValues::ClassMethods#convert

Defined in:
lib/convertable_values.rb

#convert(value_attr, unit_attr) ⇒ Object

Calling convert(value_attr_name, unit_attr_name) will set up that pair of value/unit attributes to automatically convert the valu to/from the given unit’s base unit.



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# File 'lib/convertable_values.rb', line 14

def convert(value_attr, unit_attr)
  # Create override method for converting value to base unit when set
  define_method "#{value_attr}=".to_sym do |new_value|
    new_value = new_value.to_f if new_value.is_a?(String)
    unit_str = send(unit_attr.to_sym)
    
    if new_value && unit_str
      # store the value converted to the base unit corresponding to the given unit
      if respond_to?(:write_attribute, true)
        write_attribute(value_attr.to_sym, new_value.send(unit_str))
      else
        instance_variable_set("@#{value_attr}".to_sym, new_value.send(unit_str))
      end
    else
      if respond_to?(:write_attribute, true)
        write_attribute(value_attr.to_sym, new_value)
      else
        instance_variable_set("@#{value_attr}".to_sym, new_value)
      end
    end
  end
  
  # Create override method for converting value to stored unit when accessed
  define_method value_attr.to_sym do
    unit_str = send(unit_attr.to_sym)
    
    if unit_str
      # return the value converted back to whatever unit was stored
      if respond_to?(:read_attribute, true)
        read_attribute(value_attr.to_sym).to(unit_str.to_sym)
      else
        instance_variable_get("@#{value_attr}".to_sym).to(unit_str.to_sym)
      end
    else
      if respond_to?(:read_attribute, true)
        read_attribute(value_attr.to_sym)
      else
        instance_variable_get("@#{value_attr}".to_sym)
      end
    end
  end
  
  # Create override method for updating value when unit is set/changed
  define_method "#{unit_attr}=".to_sym do |new_unit|
    if respond_to?(:read_attribute, true)
      old_unit = read_attribute(unit_attr.to_sym)
    else
      old_unit = instance_variable_get("@#{unit_attr}".to_sym)
    end
    
    if respond_to?(:write_attribute, true)
      write_attribute(unit_attr.to_sym, new_unit)
    else
      instance_variable_set("@#{unit_attr}".to_sym, new_unit)
    end
  
    # Re-assign the value so it will be converted properly
    if respond_to?(:read_attribute, true)
      value = read_attribute(value_attr.to_sym)
    else
      value = instance_variable_get("@#{value_attr}".to_sym)
    end
    send("#{value_attr}=".to_sym, value) if value && old_unit.nil?

    new_unit
  end
end