case_class

Case class macros for the Crystal Language.

Installation

Add this to your application's shard.yml:

dependencies:
  case_class:
    github: lbarasti/case_class

Usage

require "case_class"

Defining a class with read-only fields is as easy as

case_class Person{name : String, age : Int = 18}

Case classes also define a human readable string representation for the class

p = Person.new("Rick", 28)
puts p # prints "Person(Rick, 28)"

If you're into ADTs, then you will enjoy case_class support for inheritance. Here is a sample implementation for a calculator data types.

abstract class Expr(T)
end

case_class IntExpr{value : Int32} < Expr(Int32)

case_class BoolExpr{value : Bool} < Expr(Bool)

case_class Add{a : Expr(Int32), b : Expr(Int32)} < Expr(Int32)

case_class Eq{a : Expr(Int32), b : Expr(Int32)} < Expr(Bool)

Known Limitations

• case_class definition must have at least one argument. This is by design. Use class NoArgClass; end instead.
• case_class definitions are body-free. If you want to define additonal methods on a case class, then just re-open the definition:

case_class YourClass{id : String}

class YourClass
  # additional methods here
end

Development

To expand the macro

crystal tool expand -c <path/to/file.cr>:<line>:<col> <path/to/file.cr>

Contributing

1. Fork it ( https://github.com/lbarasti/case_class/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• lbarasti - creator, maintainer