[go-nuts] curiosity - why write a function to do this?

Append essentially does the following: http://play.golang.org/p/WFaGXhFvlc

My guess is that there are three reasons to have cloneBytes:

1. If you notice the created new slice in append has extra capacity (to
be used on further appends), but it seems this use case is meant to copy a
slice (no extra space needed)
2. The comparison inside cloneBytes is simpler than in append (compare
to 0), and may get optimized out after inlining (the calling code already
checks for nil in some points)
3. In the real append, the amount of extra space is not a constant
number of additional elements or a constant scale, but is chosen based on
slice size resulting in at least one extra branch in the code

In the CL referenced it looks like the purpose of cloneBytes is to make a
copy of the data that is not going to be appended to. Although #2 and #3
may be able to go away in certain places with a good compiler, #1 will
always be true, as append will always allocated some extra slots in case of
future appends, to avoid the allocations and copies involved in appending
to a full slice.

cloneBytes(b) can be replaced by(or implemented as) append([[]byte(nil),
b...)

David

It preserves the nil-ness.

With append: http://play.golang.org/p/Kf27Wthe23

Ahhhh, I only looked at t from the other direction. Thanks.

When I run that, it tells me "nil=true" for both code paths.

So it would appear that append() also preserves nil as long as you are
actually appending nothing.

John
=:->

It preserves the state of nil-ness in the original slice. Try replacing the append with the cloneBytes func and see where they differ.