Duck typed maths filters

[ismasan]

What

Allow maths filters to work with objects that respond to #to_number as well as things that can be coerced into numbers.

Why

So I can design my own complex types or Drops that can work with maths filters.

How

If an object responds to #to_number, it will be used by Utils.to_number when coercing values.

An example:

class PriceDrop < Liquid::Drop
  def initialize(amount, currency_symbol)
    @amount, @currency_symbol = product_price, currency_symbol
  end

  def formatted
    "#{@currency_symbol}#{@amount}"
  end

  # .. etc, other methods here

  # this makes it work with Liquid's maths filters
  def to_number
    @amount
  end
end

Now it can be used with maths filters

price = PriceDrop.new(1000.0, '$')
template = Liquid::Template.parse("net total: {{ price.formatted }}. Tax: {{ price | times: 0.19 }}")
template.render('price' => price) # => "net total: $1000.0. Tax: 190"

Notes / questions

• Standard text filters already use duck typing (by calling #to_s on the object), but Utils.to_number, used to coerce values in maths filters, does not. I am not sure whether or not this limitation is by design / security reasons, so I'm putting this here up for discussion.
• I went with #to_number instead of a more conventional #to_i or #to_f to avoid accidental coercion (as many types in Ruby-land implement those) and also to mirror Utils.to_number. Please advice if this is not a good idea.

[fw42]

I'm not against this... Seems useful to me. @pushrax, @dylanahsmith, thoughts?

[dylanahsmith]

Sounds good to me

[pushrax]

Thanks for the contribution!

[ismasan]

Thank you guys for Liquid! Do we have an idea re. when the next release is going to be?