Print type of variable

Using Swift
1

We can print the type of a value/object:

class A {}
class B: A {}

func getA() -> A {
    return B()
}

let a = getA()
print(type(of: a)) // B

I was wondering whether it is possible to print the type of the variable. So, instead of printing 'B', it would print 'A', the type that has been inferred for 'a'.

2

If all that you want is to know the inferred type of a variable, and that you use Xcode, and that you feel lucky, alt-click the variable name. Xcode will display its inferred type:

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Unfortunately, Xcode will not always perform this task correctly. Sometimes it will fail displaying the desired information.

3

Not sure what your use case for this is, but you could always use a generic function – the placeholder of which is satisfied by the static type of the argument passed, for example:

class A {}
class B : A {}

func getA() -> A {
  return B()
}

func printStaticType<T>(of _: T) {
  print(T.self)
}

let a = getA()
printStaticType(of: a) // A
2 Likes
4

I just ran into this when I copied some code into an online compiler and I wondered what type was inferred.

Nice solution, I didn't think of that.

I guess there is no standard way to do this. Would it be worthwhile to add this to the standard library?

5

I guess it would be something like this then:

func staticType<T>(of _: T) -> String {
    return String(describing: T.self)
}
6

It should return a type instead of a String, just like type(of:)

7

Ah, I always thought type(of:) just returned a String! Second attempt:

func staticType<T>(of _: T) -> T.Type {
    return T.self
}
1 Like
8

Not sure what others think (you could always float it on evolution/pitches), but personally I think this is better done through tooling than the standard library. I don't know how straightforward it is currently, but I believe such online playgrounds should be able to use SourceKit in order to request doc info and use that in order to show the inferred types of declarations.

1 Like
9

I created a pitch: