Loading data into an index with a different metric silently fails

[scottbreyfogle]

The title basically says it. If you try to load an index with a different metric, it seems that the system should either try and recover (maybe not possible), or return False/show an error. Instead, it silently creates an empty tree.

Steps to reproduce:

from annoy import AnnoyIndex
PATH = "/tmp/test.ann"

i = AnnoyIndex(2,metric="euclidean")
i.add_item(0,[1,2])
i.build(1) # Returns True
i.save(PATH) # Returns True

i2=AnnoyIndex(2)
i2.load(PATH) # Returns True
assert i.get_n_items() == i2.get_n_items()

[erikbern]

there's no foolproof way to catch that the metric isn't right (it's not stored inside the index)

that being said there's a few tricks you can use so maybe we should add those