On 12/30/17 8:57 PM, Tony wrote:
For me, it is confusing to use "slice" and "dynamic array" as synonyms. My initial impression was that they must have different code underlying them, and different behavior.
As stated in the slices article, I think of them as separate -- the slice is the public type that is used to operate on dynamic arrays, the dynamic array is a nameless type that only exists in the runtime. It helped me immensely when rewriting the array runtime to think of it that way. All the feedback I received when publishing the article was along the lines of "Wow, thinking of it that way helps a lot", so I think it's a good mental model.
But in terms of D types, the slice *is* the dynamic array type, it behaves in all the ways you would expect a dynamic array type to behave. The only difference is that a slice does not own the memory it references. Normally you would consider a dynamic array to own its memory (i.e. be responsible for allocation and destruction). Because we have the GC, ownership can be fuzzy.
The DLang Tour has a section on Slices that says in bold "Slices and dynamic arrays are the same". I think that sentence deserves an explanation as to why there are two terms being utilized for the same thing. I would prefer that "slice" as a noun was used only for the time when a dynamic array was initialized from a slice of another array. Or better yet - slice was never used as a noun - only a verb or adjective: took a slice of array A to form a slice dynamic array B (or slice-intialized dynamic array B).
The question really is, what is the name of the type T[]? If you give it a different name depending on how it was created, then you have all sorts of confusion. In fact, there was a proposal by Walter and Andrei a long long time ago to have a type T[new] which would be the dynamic array type, and T[] be the slice type. This failed, because in Andrei's words, "Explaining two very similar but subtly different types to newcomers is excruciatingly difficult."
IMO, T[] is a slice, because it may not be GC-backed dynamic array data underneath. Some people prefer to think of it as a dynamic array, because you can use it like a dynamic array no matter what it points at. Either way works, and fits the implementation. It's really a matter of preference.
-Steve
