如何在Closure中为函数调用指定泛型类型参数？

Question

I am working on reducing the use of accidentally-unknown generic type parameters in a code base. I am using a Closure TTL incantation like the following to coerce unknown generic types to the undefined type, hopefully provoking errors that let me find these cases (see this related question ).

 * @template T
 * @template TYPE_I_ACTUALLY_USE := cond(isUnknown(T), 'undefined', T) =:

That has brought me to a case like this:

/**
 * @template T
 * @template R := cond(isUnknown(T), 'undefined', T) =: 
 * @param {function():R} factory
 * @return {{prop: R}}
 */
function factoryWrapper(factory) {
  return {prop: factory()};
}

var instance = factoryWrapper(() => 2);

This factoryWrapper function takes a factory function that produces a value of type R , calls it, and wraps the result in {prop: ...} , for a return type of {prop: R} . But because I don't specify T or R when calling factoryWrapper , it doesn't know what type they're supposed to be, and can't tell whether the provided factory function returns the right type, so it produces an error or untyped output:

input0:11: WARNING - inconsistent return type
found   : number
required: undefined
var instance = factoryWrapper(() => 2);

In a language with a native type annotation syntax, like TypeScript, I might fix this by including the generic type parameter in the invocation:

var instance = factoryWrapper<number>(() => 2);

However, I haven't been able to figure out any equivalent syntax for Closure. I took a few guesses, like the following, but none worked.

var instance = factoryWrapper/** <number> */(() => 2);

How do I specify generic type parameters for a function invocation in Closure JavaScript?

Answer 1

Closure Compiler doesn't allow you to specify type parameters when calling a generic function. But I think casting the callback will do what you want. Something like: var instance = factoryWrapper(/** @type {function(): number} */ (() => 2));