add support for dtype kinds in `astype`

[lucascolley]

data-apis/array-api#848 (comment)

[ev-br]

This seems to have slipped under the radar. Could you remind me what are the motivating use cases? IIUC, one was float32->complex64, which is now IMO adequately handled by 1j*float32_array -> complex64_array. Was there something about signed/unsigned integers? My search-foo is failing me

[lucascolley]

Hmm, not sure if there was a real-world motivating case for signed/unsigned integers, but in general I still think this is rather nice to have. Suppose you are using something like this in a context of parametrising over dtype kinds, something like

dtype_id = 1.0 if dtype_kind=="float" else 1j # or more cases
x *= dtype_id

can become

x = xp.astype(x, kind=dtype_kind)

which is not only cleaner but also semantically much nicer IMO!

[ev-br]

This is the int/uint discussion I was trying to remember:
data-apis/array-api#859 (comment)

[lucascolley]

any further thoughts @ev-br ?