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$ gem install definition
Fetching: definition-0.5.1.gem (100%)
Successfully installed definition-0.5.1
Parsing documentation for definition-0.5.1
Installing ri documentation for definition-0.5.1
Done installing documentation for definition after 0 seconds
1 gem installed
$ irb
2.5.1 :001 > require "definition"
Traceback (most recent call last):
9: from /home/nih/.rvm/rubies/ruby-2.5.1/bin/irb:11:in <main>' 8: from (irb):1 7: from /home/nih/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:39:in require'
6: from /home/nih/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:135:in rescue in require' 5: from /home/nih/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:135:in require'
4: from /home/nih/.rvm/gems/ruby-2.5.1/gems/definition-0.5.1/lib/definition.rb:8:in <top (required)>' 3: from /home/nih/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:70:in require'
2: from /home/nih/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:70:in require' 1: from /home/nih/.rvm/gems/ruby-2.5.1/gems/definition-0.5.1/lib/definition/i18n.rb:3:in <top (required)>'
NoMethodError (undefined method `Pathname' for main:Object)

Error messages should be easy to map to a source like for example a form field or a path in a json document. Also one needs to generate a translated error message for each error

... like string length checks (min/max), non empty strings checks, gt, lt and maybe more

If a Lambda definition fails then it currently returns a rather generic error message that only mentions the name of the lambda. This is not providing enough information to users to correct the bad input in some cases though. for example when building a definition that checks if a provided array includes only uniqe values then you might want to point out which value is not unique:

::Definition::Lambda(:unique_values) do |array|
  next unless array.uniq.size == array.size

  conform_with(array)
end

In this case something like this would be nice:

::Definition::Lambda(:unique_values) do |array|
  duplicates = array.select{ |e| array.count(e) > 1 }.uniq

  if duplicates.empty?
    conform_with(array)
  else
    fail_with("Array contains duplicate values: #{duplicates.join(', ')}")
  end
end

At the same time the version without fail_with should still work

Other usecases that come to mind:

• An array needs to contain some specific items and you want to tell the user which ones are missing
• You do validation across multiple fields, e.g. If field A is present, then field B must be present as well

definition = Definition.Or(
  Definition.Keys do
    required(:person, Definition.Keys do
      required(:first_name, Definition.Type(String))
    end) 
  end,
  Definition.Keys do
    required(:social_security_number, Definition.Type(String))
  end
)

definition.conform({ person: { first_name: 1 } }).error_hash => {
  "person": null,
  "social_security_number": [
    "<Definition::ConformError \n\t message: \"hash is missing key :social_security_number\", \n\t json_pointer: \"/social_security_number\">"
  ]
}

the returned errors are correct, just the error_hash representation not.

❤️

The #to_s method of ConformError suggests an API that doesn't exist: (also there's a typo)

I'd suggest that the class should define those two methods or be stringified in a different way.

Provide functionality to define and validate the initialization arguments of a class in an easy way. e.g.

class MyClass
  include Definition::Initializer

  required :username, Definition.Type(String)
  optional :scores, Definition.Type(Array)

  def hello
    puts "Hello #{username}"
  end
end

instance = MyClass.new(username: "Fred", scores: [1,2,3])
instance.hello # => "Hello Fred"

this would only support keyword arguments though

Feedback welcome :)

Currently you cannot define defaults for Key Definitions