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from typing import Any, TypeVar
_T = TypeVar("_T")
class SingletonMeta(type):
"""Metaclass for singleton pattern."""
# We store instances keyed by the class type
_instances: dict[type, object] = {}
def __call__(cls: type[_T], *args: Any, **kwargs: Any) -> _T:
"""Call method for the singleton metaclass.
Args:
cls: The class being instantiated.
*args: Positional arguments for the class constructor.
**kwargs: Keyword arguments for the class constructor.
Returns:
The singleton instance of the class.
"""
# Use SingletonMeta._instances to access the class attribute
if cls not in SingletonMeta._instances: # pyright: ignore[reportUnnecessaryContains]
# Create the instance using super().__call__ which calls the class's __new__ and __init__
instance = super().__call__(*args, **kwargs) # type: ignore
SingletonMeta._instances[cls] = instance
# Return the cached instance. We cast here because the dictionary stores `object`,
# but we know it's of type _T for the given cls key.
# Mypy might need an ignore here depending on configuration, but pyright should handle it.
return SingletonMeta._instances[cls] # type: ignore[return-value]
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