Accessing Attributes of Subclasses

[01110011011101010110010001101111]

Hello! I'm trying to access attributes of subclasses. For example, I'm trying to run something like this:

@dataclass
class Statement:
    pass

@dataclass
class Block(Statement):
    bodies: list[str]

@dataclass
class Assign(Statement):
    var: str
    val: Statement

@dataclass
class Function:
    name: str
    body: Statement

func_body = Block(bodies=["a = 1", "return a"])

test = Function(
        name="foo", 
        body=func_body
)

v1 = test.body

if isinstance(v1, Block):
    bodies = v1.bodies
    if bodies is not None:
        for stmt in bodies:
            print(stmt)
    else:
        print("fail")

For the above example, if the body attribute of the Function class is a Block, I want to be able to iterate through the values in its bodies attribute. The above fails with codon_experiments.py:39 (14-23): error: 'Statement' object has no attribute 'bodies'.

I instead tried to use a Union with NoneType in the parent class:

@dataclass
class Statement:
    bodies: list[str] | NoneType = None
    var: str | NoneType = None
    val: Statement | NoneType = None

@dataclass
class Block(Statement):
    bodies: list[str] | NoneType

@dataclass
class Assign(Statement):
    var: str | NoneType
    val: Statement | NoneType

@dataclass
class Function:
    name: str
    body: Statement

func_body = Block(bodies=["a = 1", "return a"])

test = Function(
        name="foo", 
        body=func_body
)

v1 = test.body

if isinstance(v1, Block):
    bodies = v1.bodies
    if bodies is not None:
        for stmt in bodies:
            print(stmt)
    else:
        print("fail")

The above, however, fails with:

Assert failed:  union already sealed [core.codon:237:1]
Expression:     !isSealed()
Source:         /github/workspace/codon/parser/ast/types/union.cpp:107
Aborted (core dumped)

Finally, I tried to use the Optional type but this resulted in the value always being None:

@dataclass
class Statement:
    bodies: Optional[list[str]] = None
    var: Optional[str] = None
    val: Optional[Statement] = None

@dataclass
class Block(Statement):
    bodies: Optional[list[str]]

@dataclass
class Assign(Statement):
    var: Optional[str]
    val: Optional[Statement]

@dataclass
class Function:
    name: str
    body: Statement

func_body = Block(bodies=["a = 1", "return a"])

test = Function(
        name="foo", 
        body=func_body
)

v1 = test.body

if isinstance(v1, Block):
    bodies = v1.bodies
    if bodies is not None:
        for stmt in bodies:
            print(stmt)
    else:
        print("fail")

The above compiles and runs but always prints fail.

Do you have any suggestions on how to approach this? Thanks!

[BI71317]

Hi, @01110011011101010110010001101111

Like before, Seems interesting problem.

To be clear, As codon is ahead of time language, strict type model is required.

If you need to access fields directly (in this case, string type), Statement Type Should be that class type self:

@dataclass
class Block:
    bodies: list[str]

@dataclass
class Assign:
    var: str
    val: str

Statement = Union[Block, Assign]

@dataclass
class Function:
    name: str
    body: Statement

func_body: Statement = Block(bodies=["a = 1", "return a"])
test = Function(name="foo", body=func_body)

v1 = test.body

if isinstance(v1, Block):
    for stmt in v1.bodies:
        print(stmt)
elif isinstance(v1, Assign):
    print(v1.var, v1.val)

But if it's not that case, and if you can tolerate in more abstracted way to access to fields, then below might be suitable for case:

class Statement:
    def dump(self):
        print("<statement>")

class Block(Statement):
    bodies: list[str]

    def __init__(self, bodies: list[str]):
        self.bodies = bodies

    def dump(self):
        for stmt in self.bodies:
            print(stmt)

class Assign(Statement):
    var: str
    val: str

    def __init__(self, var: str, val: str):
        self.var = var
        self.val = val

    def dump(self):
        print(f"{self.var} = {self.val}")

class Function:
    name: str
    body: Statement

    def __init__(self, name: str, body: Statement):
        self.name = name
        self.body = body

func_body = Block(["a = 1", "return a"])
test = Function("foo", func_body)
test.body.dump()

I hope this comment resolves your curiosity, thanks.