is there a good way to copy as much as possible from a long slice into a short slice?

ie. you have a slice pointing to a [u8; 123] and you want to copy the first portion of it into a slice pointing to a [u8; 45]

I know we can manually do range bound arthritic. Iterators probably can do it too without much hassle.
Are there any other simple ways to do it?
I feel like there ought to be some standard library function for this that is less error prone / complex than the methods I mentioned above