CODEWITHSUNDEEP
typescript
Rox
Rox

Reputation: 2917

Compiler error in Typescript version 3 but not in version 2

Since updating Typescript to 3.x I can not compile this class anymore:

class MyClass<T>{
    private myMethods: [(val: T) => void] = [] as [(val: T) => void];
}

More specific, it is [] as [(val: T) => void] that triggers the error and the compiler message is:

Error:(7, 47) TS2352: Type '[]' cannot be converted to type '[(val: T) => void]'.
  Property '0' is missing in type '[]'.

It DO work in Typescript 2.9.2 though!

So what is the problem here and how do I solve it?

Upvotes: 0

Views: 72

Answers (2)

Oblosys
Oblosys

Reputation: 15106

If myMethods is not a tuple but an array (as the name suggests,) you can just do

class MyClass<T>{
    private myMethods: Array<(val: T) => void> = [];
}

Upvotes: 1

Akash Kava
Akash Kava

Reputation: 39916

This is due to tuple length enforcement in TypeScript 3.0 which forces signature [T] to have one element in the array of type T.

The only solution is to make an element type optional as follow.

class MyClass<T>{
    private myMethods: [((val: T) => void)?] = [] as [((val: T) => void)?];
}

Upvotes: 1

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