Newbie question about return value of == operator

[Blue Hand Talking]

I wonder if someone could explain how the '==' comparison operator
is being used below,
not quite getting it, or even the general flow.

Properties of Class Order:

attr_accessible :line_items
has_many :line_items
accepts_nested_attributes_for :line_items




def compute_order(order)
matched_line_items = order.line_items.select do |line_item|
line_item.product.tax_category == rate.tax_category
end

line_items_total = matched_line_items.sum(&:total)
round_to_two_places(line_items_total * rate.amount)
end


Would 'matched_line_items' be an array of product objects with
their tax_category value set from this operation?

If so, how is this happening? Seems that the comparison would be
returning true or false.

Also, here is Product#tax_category method:

def tax_category
if self[:tax_category_id].nil?
TaxCategory.whereis_default => true).first
else
TaxCategory.find(self[:tax_category_id])
end
end

Thanks,

Jet

 

[Robert Klemme]

I wonder if someone could explain how the '==' comparison operator
is being used below,
not quite getting it, or even the general flow.

Properties of Class Order:

attr_accessible :line_items
has_many :line_items
accepts_nested_attributes_for :line_items




def compute_order(order)
matched_line_items = order.line_items.select do |line_item|
line_item.product.tax_category == rate.tax_category
end

line_items_total = matched_line_items.sum(&:total)
round_to_two_places(line_items_total * rate.amount)
end


Would 'matched_line_items' be an array of product objects with
their tax_category value set from this operation?

Normally not since #== usually works read only. On face value
matched_line_items are all elements from order.line_items which have a
product with tax_category equal to rate.tax_category.

If so, how is this happening? Seems that the comparison would be
returning true or false.

Right. Actually #== can return anything - Ruby will treat false and nil
as false and everything else as true.

Cheers

robert

 

[Simon Krahnke]

I wonder if someone could explain how the '==' comparison operator
is being used below,
not quite getting it, or even the general flow.

Properties of Class Order:

attr_accessible :line_items
has_many :line_items
accepts_nested_attributes_for :line_items




def compute_order(order)
matched_line_items = order.line_items.select do |line_item|
line_item.product.tax_category == rate.tax_category
end

line_items_total = matched_line_items.sum(&:total)
round_to_two_places(line_items_total * rate.amount)
end

The select method on an array works by returning an array of the
elements for which the block returns true. do introduces such a block.

That means matched_line_items are the order.line_items for which the
line_item's product's tax_category is the same as rate.tax_category.

mfg, simon .... hth

 

[Blue Hand Talking]

Robert and Simon,

Thank you both. did read the documentation on select,
but evidently did not mull over it enough.

/****************************************/

select {|item| block } → an_array

Invokes the block passing in successive elements from array, returning
an array containing those elements for which the block returns a true
value (equivalent to Enumerable#select).

/****************************************/


Hmm, looks pretty straight forward this time

Cheers,

Jet

 

[Robert Klemme]

Robert and Simon,

Thank you both. did read the documentation on select,
but evidently did not mull over it enough.

You're welcome!

/****************************************/

select {|item| block } → an_array

Invokes the block passing in successive elements from array, returning
an array containing those elements for which the block returns a true
value (equivalent to Enumerable#select).

/****************************************/


Hmm, looks pretty straight forward this time

Apparently that always happens in hindsight.

Cheers

robert