Proposal: Follow program flow in constructor when strictPropertyInitialization = true

Search Terms

constructor strictPropertyInitialization flow

Suggestion

TypeScript should follow unconditional function calls in constructor when checking for strict property initialization.

Use Cases

It is a common pattern to be able to reset objects after construction and, thus, to transfer object initialization to a separate routine:

class C
{
  private p: number;

  public constructor() { Initialize() }

  public Initialize() { p = 0; }
}

Currently, TypeScript doesn't consider functions being unconditionally called from within a constructor function when checking for strict property initialization. The above code yields a compiler error.

I propose TypeScript to be able to analyse code flow and recognize property initialization that's performed in functions unconditionally called by the constructor function.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Start by tracing the compiler's strictPropertyInitialization checks for constructors and unconditional function calls; the issue names no files or tests. Determine how control flow through a separately defined Initialize method should affect property initialization, then add coverage showing that the example is accepted while non-unconditional calls remain rejected.