# Object

All data that can be assigned to a variable. The attributes of the `Object` class are as follows.

* `.__repr__`: Returns a (non-rich) string representation of the object
* `.__sizeof__`: Returns the size of the object (including heap allocation)
* `.__dir__`: Returns a list of object attributes
* `.__hash__`: returns the hash value of the object
* `.__getattribute__`: Get and return an attribute of an object
* `.clone`: Creates and returns a clone of an object (with an independent entity in memory)
* `.copy`: Returns a copy of the object (pointing to the same thing in memory)

## Record

An object generated by a record literal (`{attr = value; ...}`).
This object has basic methods such as `.clone` and `.__sizeof__`.

```python
obj = {.x = 1}
assert obj.x == 1

obj2 = {...x; .y = 2}
assert obj2.x == 1 and obj2.y == 2
```

## Attribute

An object associated with an object. In particular, a subroutine attribute that takes self (`self`) as its implicit first argument is called a method.

```python
# note that there is no `.` in private_attr
record = {.public_attr = j; private_attr = 2; .method = self -> self.i + 1}
record. public_attr == 2
record.private_attr # AttributeError: private_attr is private
assert record.method() == 3
```

## Element

An object belonging to a particular type (e.g. `1` is an element of type `Int`). All objects are at least elements of type `{=}`.
Elements of classes are sometimes called instances.

## Subroutine

Indicates an object that is an instance of a function or procedure (including methods). The class representing a subroutine is `Subroutine`.
An object that implements `.__call__` is more commonly called a `Callable`.

## Callable

An object that implements `.__call__`. It is also the superclass of `Subroutine`.

## Type

An object that defines requirement attributes and commonizes objects.
There are two main types: Polymorphic Type and Monomorphic Type. Typical monomorphic types are `Int`, `Str`, etc., and polymorphic types are `Option Int`, `[Int; 3]`, etc.
Furthermore, a type that defines a method that changes the state of an object is called a Mutable type, and it is necessary to add `!` to the variable attribute (e.g. dynamic array: `[T; !_]`) .

## Class

A type that has `.__new__`, `.__init__` methods, etc. Implement class-based object orientation.

## Function

A subroutine that has read permission for external variables (excluding static variables) but does not have read/write permission for external variables. In other words, it has no external side effects.
Erg functions are defined differently than Python's because they do not allow side effects.

## Procedure

It has read and `self` permissions for external variables, read/write permissions for static variables, and is allowed to use all subroutines. It can have external side effects.

## Method

A subroutine that implicitly takes `self` as the first argument. It is a different type than a simple function/procedure.

## Entity

Objects that are not subroutines and types.
Monomorphic entities (`1`, `"a"`, etc.) are also called value objects, polymorphic entities (`[1, 2, 3], {"a": 1}`) are also called container objects .

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