Tensor subclass boilerplate can be consolidated

[HDCharles]

A lot of code for tensor subclasses can likely be conslidated together into a base class that other classes can utilize

_get_to_kwargs:
https://github.com/pytorch/ao/blob/main/torchao/dtypes/affine_quantized_tensor.py#L64
https://github.com/pytorch/ao/blob/main/torchao/dtypes/affine_quantized_tensor.py#L276
(also needed for https://github.com/pytorch/ao/blob/main/torchao/quantization/autoquant.py#L40)

to:
https://github.com/pytorch/ao/blob/main/torchao/dtypes/affine_quantized_tensor.py#L594
https://github.com/pytorch/ao/blob/main/torchao/dtypes/affine_quantized_tensor.py#L290
https://github.com/pytorch/ao/blob/main/torchao/dtypes/affine_quantized_tensor.py#L423
(also needed for https://github.com/pytorch/ao/blob/main/torchao/quantization/autoquant.py#L40)

_apply_fn_to_data:
https://github.com/pytorch/ao/blob/main/torchao/dtypes/affine_quantized_tensor.py#L432

detach:
https://github.com/pytorch/ao/blob/main/torchao/dtypes/affine_quantized_tensor.py#L444

a default repr would be nice (it caused bugs in the past)

if these were implemented using tensor_flatten and tensor_unflatten e.g. https://github.com/pytorch/ao/blob/main/torchao/dtypes/affine_quantized_tensor.py#L412-L421
you could write a general mixin/parent class that handles the general form of those methods

[HDCharles]

@jerry39213gh thoughts?

[jerryzh168]

yes, this makes sense I think, we can put this https://github.com/pytorch/ao/blob/main/torchao/dtypes/utils.py. we can also attach

ao/torchao/quantization/linear_activation_quantized_tensor.py

Lines 98 to 100 in ac8ce4c

	implements = classmethod(_implements)
	__torch_function__ = classmethod(_dispatch__torch_function__)
	__torch_dispatch__ = classmethod(_dispatch__torch_dispatch__)

by default

there could be some issues of child class modifying the dispatch table for parent class, if this becomes an issue, we can add class to the dispatch table as well in the future.