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TypeCheck

This library provides a minimal interface to perform type comparisons beteween a literal value and a type constraint. It draws heavily from a LiveScript library called type-check.

gem install type_check

Quick examples

require 'type_check'

## Basic types
TypeCheck::valid?(Integer, 42)            # true
TypeCheck::valid?(Integer, "42")          # false
TypeCheck::valid?(Integer, "42")          # false
TypeCheck::valid?(NilClass, nil)          # true
TypeCheck::valid?(Hash, { answer: 42 })   # true
TypeCheck::valid?(Array, ["foo", "bar"])  # true
TypeCheck::valid?(Array, "Array")         # false
## Optional types
TypeCheck::valid?([Integer, String], 42)              # true
TypeCheck::valid?([Integer, String], "42")            # true
TypeCheck::valid?([Integer, String], { answer: 42 })  # false
TypeCheck::valid?([NilClass, String], nil)            # true

Usage

POR

The basic hash-to-rules comparison operation can be used anywhere, e.g. a Sinatra endpoint. Generally speaking, the following pattern could be useful anywhere you want to enforce type constraints on an input object/document as part of permitting the operation to proceed.

TypeConstraints = {
  input_1: String,
  input_2: Integer,
  optional_input_3: [NilClass, String]
}.freeze

def business_sensitive_operation!(inputs)
  errors = type_check_params(TypeConstraints, inputs)
  raise(BadInputsError) if errors.present?
  # proceed with the remaining operations
  ...
end

Rails

The salient methods in the following code snippet are:

  • type_check_params: when used in a before_action, this method will compare each type constraint in CreateUserParams to the corresponding parameter value. Fail states can and should be handled by yielding to a block, where you have access to the parameters' validation errors.
  • filtered_params: removes non-permitted parameters, returning only key-value pairs specified in the type constraints. This method will raise an exception if called prior to type_check_params This method will raise an exception if called prior to type_check_params.
class UsersController < ActionController::Base
  include TypeCheck::ActionController

  CreateUserParams = {
    name:  String,      # params[:name] is a required string parameter
    email: String,      # params[:email] is a required string parameter
    age:   Integer      # params[:age] is a required numeric parameter
  }.freeze

  type_check_params CreateUserParams, only: :create do |errors|
    # Handle fail states inside this block.
    return render json: errors, status: 400
  end

  def create
    user = User.new(filtered_params)
  end
end

License

The gem is available as open source under the terms of the MIT License.