question: How can I validate a union of strings?

**I was trying to...**
use ```export type ValidateValues = ‘val1’ | ‘val2’ | ‘val3’;```
with @Type to make sure the values are correct

**The problem:**

```
@Type((_) => ValidateValues)
'ValidateValues' only refers to a type, but is being used as a value here
```

PS: I was trying to avoid using a enum