QuickStruct

Macro to create data structures as structs with less boilerplate.

Installation

First, add QuickStruct to your mix.exs dependencies:

def deps do
  [{:quick_struct, "~> 0.1"}]
end

and run $ mix deps.get.

Usage

defmodule User do
  use QuickStruct, [firstname: String.t, name: String.t]
end

Now you can use User.t in @type and @spec declarations. To create instances of your data structure, use one of the following options:

iex(3)> User.make("Jon", "Adams")
%User{firstname: "Jon", name: "Adams"}
iex(4)> User.make([name: "Adams", firstname: "Jon"])
%User{firstname: "Jon", name: "Adams"}
iex(5)> %User{name: "Adams", firstname: "Jon"}
%User{firstname: "Jon", name: "Adams"}

You can also define a struct without types, for instance:

defmodule QuickStructTest.Pair do
  use QuickStruct, [:first, :second]
end

Resulting code

The QuickStruct macro is a very shorthand option to define a struct, a data type and enforce all fields. The User-struct is equivalent to:

@enforce_keys [:firstname, :name]
defstruct [:firstname, :name]
@type t :: %User{firstname: String.t, name: String.t}

The macro also provides make-functions as constructors and other functions, see QuickStruct for further documentation. The generated make-functions for the User-struct are equivalent to:

@spec make(String.t, String.t) :: User.t
def make(firstname, name) do
  %User{firstname: firstname, name: name}
end

@spec make([firstname: String.t, name: String.t]) :: User.t
def make(fields) do
  Kernel.struct!(User, fields)
end

Generating predicates

The optional argument :predicate can be used to generate a predicate for the struct:

defmodule UserWithPredicate do
  use QuickStruct, [firstname: String.t, name: String.t], predicate: :user?
end

iex> user = User.make("Jon", "Adams")
%User{firstname: "Jon", name: "Adams"}
iex> User.user?(user)
true
iex> User.user?(non_user_struct)
false
iex> User.user?(1)
false

Creating modules and structs

If you need plenty of different data structures, you can use

require QuickStruct
QuickStruct.define_module(User, [firstname: String.t, name: String.t])
QuickStruct.define_module(Pair, [:first, :second])

to create a module and the corresponding struct. So this is shorthand for:

defmodule User do
  use QuickStruct, [firstname: String.t, name: String.t]
end
defmodule Pair do
  use QuickStruct, [:first, :second]
end

License

Copyright © 2021 Active Group GmbH

This work is free. You can redistribute it and/or modify it under the terms of the MIT License. See the LICENSE file for more details.