I continually struggle with typing issues, probably as I learnt to code in a polymorphic language (perl) maybe someone who understands types can help: I want to set the number of tasks in a service to the number of subnets it is being deployed to, so that the Test stack, which is deployed to 1 subnet only runs one task, but Prod, which is more redundant, runs 2 or 3 depending on how many subnets I deploy to. But at the moment Test is deployed to 2 subnets, which I will fix soon, but in order to not incur additional costs whilst I shrink Test to 1 subnet I want to override that to be 1 in the case where we are in Test. So my code:

let numTasks = vpc.publicSubnets.apply(subnets => subnets.length);

// that will work when we only have 1 subnet in the Test-vpc but for now

if (nom === 'test'){
  numTasks = 1;
}

This gives the error: stack/service.ts(14,3): error TS2322: Type '1' is not assignable to type 'Output<any>'. from the line where I try and force it to be 1 inside the if I've tried

let numTasks: number = vpc.publicSubnets.apply(subnets => subnets.length);

making it a number in the declaration but that then errors with: stack/service.ts(9,5): error TS2322: Type 'Output<any>' is not assignable to type 'number'. I'm pretty sure my code is right and that on execution subnets.length will be a number, but the typing doesn't see what is obvious to me. Anyone got any pointers on how to fix this?

let numTasks = vpc.publicSubnets.apply(subnets => subnets.length);

// that will work when we only have 1 subnet in the Test-vpc but for now

if (nom === 'test'){
  numTasks = 1;
}

When you don't define an explicit type for

numTasks

, the compiler sees that its type is the result of the

apply()

which is

Output<T>

but then later when you try to re-assign that to a

number

, it's an error.

let numTasks: number = vpc.publicSubnets.apply(subnets => subnets.length);

Here you are explicitly defining the type to be a

number

which is not correct because you are defining one type but then assigning a value of a different type,

Output<T>

. TypeScript supports union types, which allows you to do:

let numTasks: number | Output<number> = vpc.publicSubnets.apply(subnets => subnets.length);

BUT you have another option. Pulumi has a built-in type called

Input<T>

which is a union of similar to the above. It's what all resource's properties are and it's why you can either give them plain values or promise-like values.

let numTasks: Input<number> = vpc.publicSubnets.apply(subnets => subnets.length);

In this case, it sounds like

numTasks

can either be of type `Output<any>`(Which is a Pulumi-specific type), or it can be of type

number

. I think what you want is:

let numTasks: number | Output<number>

ah yes, thanks both, I'd forgoten about union types. Also useful to know that Input<T> is a union type as you say. 😄

In this case, you probably want it to be of type

pulumi.Input<number>

.

It's possible to use

pulumi.Output()

as a function? Hmm..didn't know that. TIL

No.

pulumi.Output

is a type.

pulumi.output()

is a function.