Numeric value formatting interpolation

Often we need to interpolate dynamic values inside our error messages, with different formatting styles. For exmaple display a number as currency amount "The amount $12,000 is not enough to make a purchase.".

Sometimes we also wish to preserve the value without formatting, so we can pass it as JSON data to the client.

Currently we have to do something like this:

# In model
errors.add(:foo, :bar, amount: 1000, amount_formatted: "$1,000")

# In locale file
foo:
  bar: "bar %{amount_formatted}"
  
# In JSON API controller
error_details =  errors.details[:foo].first
render json: {
  error: error_details[:error]
  amount: error_details[:amount]
}

It would be nice if we can simplify writing the formatting code somehow.

Possible Solution 1

Instead of passing numbers, pass an object instead.

errors.add(:foo, :bar, date: Format.new(date))

The object can provide two methods, one for formatting, another as raw value:

class Format
  def formatted
    @value.strftime("%D")
  end

  def raw
    @value
  end
end