class ActiveStorage::Attachment

def variant(transformations)

unknown pre-defined variant of the attachment.
Raises an +ArgumentError+ if +transformations+ is a +Symbol+ which is an

See ActiveStorage::Blob::Representable#variant for more information.
instance for the attachment with the set of +transformations+ provided.
Returns an ActiveStorage::Variant or ActiveStorage::VariantWithRecord 
def variant(transformations)
  case transformations
  when Symbol
    variant_name = transformations
    transformations = variants.fetch(variant_name) do
      record_model_name = record.to_model.model_name.name
      raise ArgumentError, "Cannot find variant :#{variant_name} for #{record_model_name}##{name}"
    end
  end
  blob.variant(transformations)
end