In Typescript what does a type annotation with two types between two curly braces mean?

Question

An example:

function doSomething(): { string, SomeClass } {
 ...
} 

From playing around with the compiler it seems that it will accept any return value that is an object with any number of string keys and SomeClass values.

So something like this:

{
 "key1": someClass1,
 "key2": someClass2,
  ...
}

Is my understanding correct?

--Update--

It seems like the annotation I need is { [key: string]: SomeClass }

Answer 1

Nope - that function signature means 'this function will return an object that has the keys string and SomeClass, and any values'. This means that this will compile fine:

function doSomething(): { string, SomeClass } {
  return {
    string: false,
    SomeClass: 1
  }
} 

It's functionally equivalent to:

function doSomething(): { string: any, SomeClass: any }