Monitoring Data Types in TypeScript for Accurate Code Interpretation

Question

Monitoring Data Types in TypeScript for Accurate Code Interpretation

I have successfully implemented a Builder design pattern in TypeScript for certain entities. One of these implementations is shown below (simplified), and can also be accessed in the playground:

type Shape = any;
type Slide = any;
type Animation = any;

export class SlideBuilder {

  private slide: Slide;

  public static start() { return new SlideBuilder(); }

  public withShape(name: string, shape: Shape): this {
    this.slide.addShape(name, shape);
    return this;
  }

  public withAnimation(name: string, animation: Animation): this {
    this.slide.addAnimation(name, animation);
    return this;
  }

  public withOrder(shape: string, animations: string[]) {
    this.slide.addOrder(shape, animations);
    return this;
  }
}

SlideBuilder
  .start()
  .withShape("Hello World", {})
  .withAnimation("Animation1", {})
  .withAnimation("Animation2", {})
  .withOrder("Could be 'Hello World' only", ["Could be 'Animation1' or 'Animation2' only"])

The challenge I am facing now is to enforce type checking to ensure that the withOrder method is called with correct parameters that were previously passed to withShape or withAnimation.

I attempted to introduce generic types to the class like so:

export class SlideBuilder<S, A> {
  withShape(name: S, shape: Shape)
  withAnimation(name: A, animation: Animation)
  withOrder(shape: S, animation: A[])
}

However, I could not figure out how to keep track of each call, such as collecting the types from individual calls into a union type. It seems necessary to somehow specify

withOrder(shape: S1 | S2 | S3 | ... | Sn)

, where Sn is a type from the withShape call. If you have any insight on how to effectively implement this, please share your thoughts.

typescript types builder

Answer 1

Answer №1

This question has been a joy to tackle!

Is it feasible for the compiler to keep track of all arguments received by a class instance's methods throughout its lifespan?

What a challenging task! Initially, I wasn't sure if it could be done.

Here is what the compiler needs to do over the duration of the class instance:

Aggregate all received arguments on each method call.
Categorize these arguments for future type checking purposes.

Let's dive in...

Solution

The approach outlined below focuses solely on method signatures, keeping them minimalistic to convey the concept effectively. Implementing the methods should be relatively straightforward.

This strategy utilizes accumulator types to monitor argument types. These accumulators resemble those used in an Array.reduce function.

Refer to the playground link and the code snippets provided:

type TrackShapes<TSlideBuilder, TNextShape> = 
  TSlideBuilder extends SlideBuilder<infer TShapes, infer TAnimations> 
  ? SlideBuilder<TShapes | TNextShape, TAnimations> 
  : never;

// Repeat similar pattern for animations...

export class SlideBuilder<TShape, TAnimation> {
    // Method implementations go here...
}

Understanding the Process

We define two accumulator types for the SlideBuilder, which extract shape and animation types from an existing instance, widen the appropriate generic type using a union, and return the modified SlideBuilder. This is the crux of the solution.

The start method initializes the SlideBuilder with 'never', essentially setting up the base state. Utilizing 'never' ensures that the union operation preserves the existing type (equivalent to adding zero).

Each invocation of withShape and withAnimation adjusts the return type based on the respective accumulator, broadening the type and organizing the argument into the correct category!

Note that the generics in withShape and withAnimation are constrained to strings, preventing unnecessary type widening and offering users a more intuitive interface without requiring as const.

The end result? Efficient tracking of argument types! The test cases below demonstrate how this fulfills the specified requirements.

Test Cases

// Passes type checking.
SlideBuilder
  .start()
  .withShape("Shape1")
  .withAnimation('Animation1')
  .withOrder("Shape1", ["Animation1"])

// Additional test cases here...

Evolution of the Approach

To explore the development journey of this solution, check out these progressive iterations:

Playground Link Initial implementation supporting shapes with as const.

Playground Link Enhancing the class with animations, eliminating the need for as const.

Playground Link Almost final version achieving the desired outcome.

Answer 2

This question has been a joy to tackle!

Is it feasible for the compiler to keep track of all arguments received by a class instance's methods throughout its lifespan?

What a challenging task! Initially, I wasn't sure if it could be done.

Here is what the compiler needs to do over the duration of the class instance:

Aggregate all received arguments on each method call.
Categorize these arguments for future type checking purposes.

Let's dive in...

Solution

The approach outlined below focuses solely on method signatures, keeping them minimalistic to convey the concept effectively. Implementing the methods should be relatively straightforward.

This strategy utilizes accumulator types to monitor argument types. These accumulators resemble those used in an Array.reduce function.

Refer to the playground link and the code snippets provided:

type TrackShapes<TSlideBuilder, TNextShape> = 
  TSlideBuilder extends SlideBuilder<infer TShapes, infer TAnimations> 
  ? SlideBuilder<TShapes | TNextShape, TAnimations> 
  : never;

// Repeat similar pattern for animations...

export class SlideBuilder<TShape, TAnimation> {
    // Method implementations go here...
}

Understanding the Process

We define two accumulator types for the SlideBuilder, which extract shape and animation types from an existing instance, widen the appropriate generic type using a union, and return the modified SlideBuilder. This is the crux of the solution.

The start method initializes the SlideBuilder with 'never', essentially setting up the base state. Utilizing 'never' ensures that the union operation preserves the existing type (equivalent to adding zero).

Each invocation of withShape and withAnimation adjusts the return type based on the respective accumulator, broadening the type and organizing the argument into the correct category!

Note that the generics in withShape and withAnimation are constrained to strings, preventing unnecessary type widening and offering users a more intuitive interface without requiring as const.

The end result? Efficient tracking of argument types! The test cases below demonstrate how this fulfills the specified requirements.

Test Cases

// Passes type checking.
SlideBuilder
  .start()
  .withShape("Shape1")
  .withAnimation('Animation1')
  .withOrder("Shape1", ["Animation1"])

// Additional test cases here...

Evolution of the Approach

To explore the development journey of this solution, check out these progressive iterations:

Playground Link Initial implementation supporting shapes with as const.

Playground Link Enhancing the class with animations, eliminating the need for as const.

Playground Link Almost final version achieving the desired outcome.

Monitoring Data Types in TypeScript for Accurate Code Interpretation

Answer №1

Solution

Understanding the Process

Test Cases

Evolution of the Approach

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