Problems with using Union types

[variux]

Hi

To give a general idea I'm working on a wrapper for sqlite3 in codon, a function takes a parameter that can takes multiple types

Ex: str, int, bool

But this little code breaks

`Param = Union[str, int, bool]
value: Param = "test"

print(type(value))`

$ codon run test.py union.codon:27 (44-45): error: __ptr__() only takes identifiers or tuple fields as arguments ├─ union.codon:92 (28-64): error: during the realization of _get_data(u: TypeWrap[Union[bool | int | str]], T: bool) ├─ str.codon:27 (20-36): error: during the realization of _str(union: TypeWrap[Union[bool | int | str]]) ├─ builtin.codon:28 (27-33): error: during the realization of __new__(what: TypeWrap[Union[bool | int | str]]) ╰─ test.py:4 (1-6): error: during the realization of print(*args: Tuple[TypeWrap[Union[bool | int | str]]], sep: str, end: str, file: Ptr[byte], flush: bool)

[arshajii]

This seems to be an issue with printing the union type itself, since the first two lines do work. You can also use e.g. isinstance(param, str) to check for a particular type.

By the way, you can do this fully at compile-time via a pattern like:

def foo(param):
    if isinstance(param, str):
        ...
    elif isinstance(param, int):
        ...
    elif isinstance(param, bool):
        ...
    else:
        # error

If you don't give param an explicit union type, then Codon can deduce the type at compile-time and only compile the appropriate if/elif branch.

[variux]

I wanted to print the type to say Type {type} is not supported but even being able to print it, it doesn't print the actual type

[yfinkelstein]

Related: #738