Make generic optional by-default and required otherwise

[rough crypt]

I'm making a class and I'd like to add an option to define the type/shape of custom data that later would be passed into functions.
How do I define a generic that by default should be empty/nothing/optional, but if it's assigned non-void type, then it should be required?

[crimson sun]

rinart73#0

Playground Link

Preview:```ts
interface BarOptions<Data = void> {
count: number
data: Data
}

class Foo<Data = void> {
bar(options: BarOptions<Data>) {}
}

const one = new Foo<string>()
one.bar({count: 10, data: "hello"})

const two = new Foo()
two.bar({count: 10}) // shouldn't error```

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[rough crypt]

Make generic optional by-default and required otherwise

[past oyster]

something like this?

[crimson sun]

that_guy977#0

Playground Link

Preview:```ts
type BarOptions<Data> = {
count: number
} & ([Data] extends [never] ? {} : {data: Data})

class Foo<Data = never> {
bar(options: BarOptions<Data>) {}
}

const one = new Foo<string>()
one.bar({count: 10, data: "hello"})

const two = new Foo()
...```

You can choose specific lines to embed by selecting them before copying the link.

[rough crypt]

Seems to work great, thank you. How do I "move" the data now when it's uncertain if it exists?