Implement class

[Smit-create]

#330

[certik]

Thanks for working on this.

[Smit-create]

@certik Does this look good?

On Python code:

class Foo:
    def __init__(self, p):
        return p

ASR:

Internal Compiler Error: Unhandled exception
Traceback (most recent call last):
  File "/Users/thebigbool/repos/lpython/src/bin/lpython.cpp", line 755
    return emit_asr(arg_file, runtime_library_dir,
  File "/Users/thebigbool/repos/lpython/src/bin/lpython.cpp", line 169
    std::cerr << diagnostics.render(input, lm, compiler_options);
  File "/Users/thebigbool/repos/lpython/src/libasr/diagnostics.cpp", line 71
    out += render_diagnostic(d, input, lm,
  File "/Users/thebigbool/repos/lpython/src/libasr/diagnostics.cpp", line 134
    populate_spans(d, lm, input);
  File "/Users/thebigbool/repos/lpython/src/libasr/diagnostics.cpp", line 121
    populate_span(s, lm, input);
  File "/Users/thebigbool/repos/lpython/src/libasr/diagnostics.cpp", line 113
    LFORTRAN_ASSERT(s.source_code.size() > 0)
AssertFailed: s.source_code.size() > 0

Also, what is the difference between Class and ClassProcedure Nodes in ASR?

[certik]

That's a bug in printing an error message, I just created an issue #398 to fix that.

Yes, I think that is a constructor. Fortran does not have constructors in this sense, so I would tackle those a little bit later. We should add whatever we need into ASR, but first let's get something like this working:

class Foo:
    def __init__(self: Foo, a: i32, b: i32, c: i32):
        self.a: i32 = a
        self.b: i32 = b
        self.c: i32 = c

    def get_a(self: Foo) -> i32:
        return self.a

I am not quite sure where you should annotate the variables inside the class, whether how I did it, or some other way.

The other thing we need are structs, which we can represent already in ASR, we just need some syntax in Python, possibly the "data classes" or whatever it is called:

@dataclass # or whatever it is called
class MyStruct:
    a: i32
    b: f64
    c: str

And it works like a struct.

[certik]

To annotate that a is an instance of the class Foo, we can do:

a: Foo
a = Foo()

[czgdp1807]

I am not quite sure where you should annotate the variables inside the class, whether how I did it, or some other way.

The way you did it seems fine.

[certik]

The Class ASR node is used for a variable type, so in here we should just remove it.

[czgdp1807]

I implemented dataclass recently in #607. So I think this can be closed.

[certik]

Well, dataclasses are implemented, but not regular classes. But we can do it later, that's a lower priority.