Do declaration merged interfaces behave differently from intersected (&) interfaces?

[fluid surge]

This example seems to give the same result. Is there some nuance I'm not aware of?

[dull bane]

Bawdy Ink Slinger#9429

Playground Link

Preview:```ts
interface Merged {
foo: string
}

interface Merged {
foo: string
bar: string
}

declare const m: Merged
m.bar
m.foo

interface A {
foo: string
}

interface B {
foo: string
bar: string
}

declare const c: A & B
c.bar
c.foo```

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[noble oriole]

now try changing the type of foo in the second declaration

[fluid surge]

oh that's strange. The first example is a compilation error, the second is a never type

Is that the only difference?

[undone sonnet]

the hover text is different too, not that that really makes much of a difference

fwiw if hover text matters there are other options:

interface Child extends Parent {} // well this has the same hover text as Merged
type Expand<T> = T extends T ? { [K in keyof T]: T[K] } : never;

on an unrelated note

generally you shouldn't be using declaration merging for types you control

since you can simply add to the original declaration

[fluid surge]

Okay that's useful information. I didn't glean that from reading the handbook. In fact, I thought there could be some way I could leverage this for internal encapsulation (I have no idea how, but it was one of the questions in my mind as I learned the concept)

Thank you both!