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| """ |
| This is a singleton metaclass that can be used to cache and re-use existing objects. |
| |
| In the Iceberg codebase we have a lot of objects that are stateless (for example Types such as StringType, |
| BooleanType etc). FixedTypes have arguments (eg. Fixed[22]) that we also make part of the key when caching |
| the newly created object. |
| |
| The Singleton uses a metaclass which essentially defines a new type. When the Type gets created, it will first |
| evaluate the `__call__` method with all the arguments. If we already initialized a class earlier, we'll just |
| return it. |
| |
| More information on metaclasses: https://docs.python.org/3/reference/datamodel.html#metaclasses |
| """ |
|
|
| from typing import Any, ClassVar, Dict |
|
|
|
|
| def _convert_to_hashable_type(element: Any) -> Any: |
| if isinstance(element, dict): |
| return tuple((_convert_to_hashable_type(k), _convert_to_hashable_type(v)) for k, v in element.items()) |
| elif isinstance(element, list): |
| return tuple(map(_convert_to_hashable_type, element)) |
| return element |
|
|
|
|
| class Singleton: |
| _instances: ClassVar[Dict] = {} |
|
|
| def __new__(cls, *args, **kwargs): |
| key = (cls, tuple(args), _convert_to_hashable_type(kwargs)) |
| if key not in cls._instances: |
| cls._instances[key] = super().__new__(cls) |
| return cls._instances[key] |
|
|
