# `Ash.TypedStruct`
[🔗](https://github.com/ash-project/ash/blob/v3.23.1/lib/ash/typed_struct.ex#L5)

A DSL for defining typed structs with field validation and constraints.

`Ash.TypedStruct` provides a convenient way to define a struct type in Ash.

Under the hood, it creates an `Ash.Type.NewType` with `subtype_of: :struct`
and the appropriate constraints.

## Example

    defmodule MyApp.UserProfile do
      use Ash.TypedStruct

      typed_struct do
        field :username, :string, allow_nil?: false
        field :email, :string, constraints: [match: ~r/@/]
        field :age, :integer, constraints: [min: 0, max: 150]
        field :bio, :string, default: ""
        field :verified, :boolean, default: false
      end
    end

    # Creating instances
    {:ok, profile} = MyApp.UserProfile.new(username: "john", email: "john@example.com")

    # Using new! for raising on errors
    profile = MyApp.UserProfile.new!(username: "jane", email: "jane@example.com", age: 25)

    # Can be used as an Ash type
    defmodule MyApp.User do
      use Ash.Resource

      attributes do
        attribute :profile, MyApp.UserProfile
      end
    end

## Field Options

* `:type` - The Ash type of the field (required)
* `:default` - Default value for the field
* `:allow_nil?` - Whether the field can be nil (defaults to `true`)
* `:constraints` - Type-specific constraints (e.g., `:min`, `:max`, `:match`)
* `:description` - Field documentation

## Constructor Functions

The generated module includes:
* `new/1` - Returns `{:ok, struct}` or `{:error, error}`
* `new!/1` - Returns the struct or raises an error

## Overriding new/1

You can override the `new/1` function to add custom logic:

    defmodule MyApp.CustomStruct do
      use Ash.TypedStruct

      typed_struct do
        field :name, :string, allow_nil?: false
        field :created_at, :utc_datetime
      end

      def new(params) do
        params = Map.put_new(params, :created_at, DateTime.utc_now())
        super(params)
      end
    end

### Options

* `:extensions` (list of module that adopts `Spark.Dsl.Extension`) - A list of DSL extensions to add to the `Spark.Dsl`

* `:otp_app` (`t:atom/0`) - The otp_app to use for any application configurable options

* `:fragments` (list of `t:module/0`) - Fragments to include in the `Spark.Dsl`. See the fragments guide for more.

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*Consult [api-reference.md](api-reference.md) for complete listing*