Effect-TS/effect @effect/schema@0.67.14

on GitHub

Patch Changes

• #2851 c5846e9 Thanks @gcanti! - Add tag and TaggedStruct constructors.

  In TypeScript tags help to enhance type discrimination and pattern matching by providing a simple yet powerful way to define and recognize different data types.

  What is a Tag?

  A tag is a literal value added to data structures, commonly used in structs, to distinguish between various object types or variants within tagged unions. This literal acts as a discriminator, making it easier to handle and process different types of data correctly and efficiently.

  Using the tag Constructor

  The tag constructor is specifically designed to create a property signature that holds a specific literal value, serving as the discriminator for object types. Here's how you can define a schema with a tag:

  import { Schema } from "@effect/schema";
  
  const User = Schema.Struct({
    _tag: Schema.tag("User"),
    name: Schema.String,
    age: Schema.Number,
  });
  
  assert.deepStrictEqual(User.make({ name: "John", age: 44 }), {
    _tag: "User",
    name: "John",
    age: 44,
  });

  In the example above, Schema.tag("User") attaches a _tag property to the User struct schema, effectively labeling objects of this struct type as "User". This label is automatically applied when using the make method to create new instances, simplifying object creation and ensuring consistent tagging.

  Simplifying Tagged Structs with TaggedStruct

  The TaggedStruct constructor streamlines the process of creating tagged structs by directly integrating the tag into the struct definition. This method provides a clearer and more declarative approach to building data structures with embedded discriminators.

  import { Schema } from "@effect/schema";
  
  const User = Schema.TaggedStruct("User", {
    name: Schema.String,
    age: Schema.Number,
  });
  
  // `_tag` is optional
  const userInstance = User.make({ name: "John", age: 44 });
  
  assert.deepStrictEqual(userInstance, {
    _tag: "User",
    name: "John",
    age: 44,
  });

  Multiple Tags

  While a primary tag is often sufficient, TypeScript allows you to define multiple tags for more complex data structuring needs. Here's an example demonstrating the use of multiple tags within a single struct:

  import { Schema } from "@effect/schema";
  
  const Product = Schema.TaggedStruct("Product", {
    category: Schema.tag("Electronics"),
    name: Schema.String,
    price: Schema.Number,
  });
  
  // `_tag` and `category` are optional
  const productInstance = Product.make({ name: "Smartphone", price: 999 });
  
  assert.deepStrictEqual(productInstance, {
    _tag: "Product",
    category: "Electronics",
    name: "Smartphone",
    price: 999,
  });

  This example showcases a product schema that not only categorizes each product under a general tag ("Product") but also specifies a category tag ("Electronics"), enhancing the clarity and specificity of the data model.