[shakow]

Because you would not have any growable vector/list structure otherwise.

The real problem is that Go merrily lets you have copy-and-append operation on a slice (good), subviews of a slice so that you can share subsets of the data without copying it (good), at the same time (very bad: any operation on either will lead to confusion).

In most languages, subslicing gives you something of another type that can't be modified (or at least not accidentally). But in Go, if I call a function `do_smth_with_slice([]byte xs)`, there is no way for me to know whether this function expects `xs` to be mutable or not.

I'm sure that e.g. a C++ function taking an std::view can do some forbidden magic to still modify the underlying data, but at least the original intent is made clear by the argument type.