What about creating a new syntax for annotating metadata? For example,
`type_hint :: metadata` could be equivalent to `Annotated[type_hint,
"metadata"]`, and if we wanted type guards to look like TypeScript they could
look like this:
```
def is_str_list(val: List[object]) -> bool :: is List[str]:
```
This might not be the best syntax, it's just one idea, but my point is that
achieving all of these goals simultaneously seems quite doable:
- Showing the actual return type
- Showing metadata
- Putting arbitrary non-Python syntax in metadata
- Retrieving the type part of the annotation at runtime as an actual type
value, not a string
- Retrieving the metadata at runtime as a string
- Avoiding the cumbersome `Annotated[]` syntax
In addition, if someone wants annotations only for other metadata and not for
types at all [1] then it's easy to just omit the type part, e.g
```
def foo(bar :: bar metadata) :: foo metadata:
```
Again, the `::` may be a bad way to do this, but the same principle of
non-type-meta-only-annotations could probably be applied to other similar
syntax proposals.
I'm sure I'm not the first to suggest something like this, but I couldn't see
anything in PEP 593. I was particularly expecting something like "New syntax"
as a section under "Rejected ideas". The closest thing is "Using (Type, Ann1,
Ann2, ...) instead of Annotated[Type, Ann1, Ann2, ...]" which felt a bit weak.
[1] e.g. as I have done in https://github.com/alexmojaki/friendly_states which
looks lovely but completely breaks mypy
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