I am used to the approach below when displaying a validation message

class Person < ApplicationRecord
  validates :bio, length: { maximum: 1000,
    too_long: "%{count} characters is the maximum allowed" }
end

However, I just found out that below is also possible. But I could not find any documentation on %<>s format. And what is the use of s found at the end?

    too_long: "%<count>s characters is the maximum allowed" }

Can someone explain the difference between these syntaxes? Or provide a documentation link on %<>s

reference:
https://guides.rubyonrails.org/active_record_validations.html#length

CodePudding user response：

That s in %<...>s denotes "string". From the sprintf docs:

For more complex formatting, Ruby supports a reference by name. %<name>s style uses format style, but %{name} style doesn't.

Example:

sprintf('%<count>s characters', count: '2,300')
=> "2,300 characters"

CodePudding user response：

Rails uses I18n internally to interpolate error messages. So for answers we should refer to its documentation. Or its source - the latter explains (hopefully) why %<>s pattern works for you.

But honestly I would avoid using non-documented features. If Rails' team decides to change the error messages interpolation machinery one day your code becomes broken - just because you relied on the internals and their non-documented features. This is unlikely to happen in this particular case, but still...