Re: Slices and Dynamic Arrays
On 01/02/2018 11:17 AM, Jonathan M Davis wrote: > On Tuesday, January 02, 2018 10:37:17 Ali Çehreli via Digitalmars-d-learn > wrote: >> For these reasons, the interface that the program is using is a "slice". >> Dynamic array is a different concept owned and implemented by the GC. > > Except that from the standpoint of the API, T[] _is_ the dynamic array - > just like std::vector is the dynamic array and not whatever its guts are - I understand your point but I think it's more confusing to call it a dynamic array in the following code: int[42] array; int[] firstHalf = array[0..$/2]; I find it simpler to see it as a slice of existing elements. In contrast, calling it a dynamic array would require explaining not to worry, no memory is being allocated; the dynamic array is backed by the stack. Not very different from calling it a slice and then explaining the GC involvement in the case of append. > Regardless, the fact that they're a container/range hybrid is what makes > this such a mess to understand. The semantics actually work fantastically if > you understand them, but it sure makes understanding them annoyingly > difficult. > > - Jonathan M Davis Agreed. Ali
Re: Slices and Dynamic Arrays
On Tuesday, January 02, 2018 10:37:17 Ali Çehreli via Digitalmars-d-learn wrote: > As soon as we call it "dynamic array", I can't help but think "adding > elements". Since GC is in the picture when that happens, it's essential > to think GC when adding an element is involved. > > Further, evident from your description it's a "slice" until you add > elements because the underlying memory e.g. can be a stack-allocated > fixed-length array. > > For these reasons, the interface that the program is using is a "slice". > Dynamic array is a different concept owned and implemented by the GC. Except that from the standpoint of the API, T[] _is_ the dynamic array - just like std::vector is the dynamic array and not whatever its guts are - and the semantics are the same whether it's backed by the GC or by a static array or by malloc-ed memory or whatever. Appending works exactly the same. Reallocation works the same. None of that changes based on whether the dynamic array is backed by GC-allocated memory or not. It's just that the capacity is guaranteed to be 0 if it isn't GC-allocated and so the first append operation is guaranteed to reallocate. The semantics of T[] itself don't change regardless, and most code doesn't need to care one whit about what kind of memory backs the dynamic array. No matter what memory backed it to start with, you get the same appending semantics. You get the same semantics when accessing the data. You get the same semantics when passing the dynamic array around. None of that depends on what kind of memory the dynamic array is a slice of. T[] functions as a dynamic array regardless of what memory backed it to start with, and as such, I completely agree with the spec calling it the dynamic array. And as soon as you start talking about T[] not being a dynamic array, you get this weird situation where T[] has all of the operations and semantics of a dynamic array, but you're not calling it a dynamic array simply because it happens to be a slice of memory that wasn't GC-allocated. So, you have this type in the type system whose semantics don't care what memory currently backs it and where code will act on it identically whether it's GC-backed or not, but folks want to then act like it's something different and treat it differently just because it happens to not be GC-backed at the moment - and the same function could be called with both GC-backed and non-GC-backed dynamic arrays. The type and its semantics are the same regardless. Of course, understanding how and when reallocation occurs matters if you want to understand the exact semantics of copying a dynamic array around or when appending or reserve is going to result in a reallocation, but that doesn't necessitate calling the GC-managed buffer the dynamic array. It just requires understanding how it's the GC that manages capacity, reserve, and appending rather than the dynamic array itself. But the API is that of a dynamic array regardless. If it weren't, you couldn't append to T[] any more than you can append to an arbitrary range. As soon as you insist on calling them slices, you're basically talking about them as if they were simply ranges rather that than the container/range hybrid that they are. Regardless, the fact that they're a container/range hybrid is what makes this such a mess to understand. The semantics actually work fantastically if you understand them, but it sure makes understanding them annoyingly difficult. - Jonathan M Davis
Re: Slices and Dynamic Arrays
First, I'm in complete agreement with Steve on this. I wrote a response to you yesterday, which I decided to not send after counting to ten because despite being much more difficult, I see that your view can also be aggreable. On 01/02/2018 10:02 AM, Jonathan M Davis wrote: > On Tuesday, January 02, 2018 07:53:00 Steven Schveighoffer via Digitalmars- > d-learn wrote: >> On 1/1/18 12:18 AM, Jonathan M Davis wrote: >>> A big problem with the term slice though is that it means more than just >>> dynamic arrays - e.g. you slice a container to get a range over it, so >>> that range is a slice of the container even though no arrays are >>> involved at all. So, you really can't rely on the term slice meaning >>> dynamic array. Whether it does or not depends on the context. That >>> means that the fact that a number of folks have taken to using the term >>> slice to mean T[] like the D Slices article talks about tends to create >>> confusion when the context is not clear. IMHO, the D Slices article >>> should be updated to use the correct terminology, but I don't think >>> that the author is willing to do that. >> The problem with all of this is that dynamic array is a defined term >> *outside* of D [1]. And it doesn't mean exactly what D calls dynamic >> arrays. >> >> This is why it's confusing to outsiders, because they are expecting the >> same thing as a C++ std::vector, or a Java/.Net ArrayList, etc. My view as well. >> And D >> "array slices" (the proper term IMO) are not the same. Exactly! >> I'm willing to change the article to mention "Array slices" instead of >> just "slices", because that is a valid criticism. But I don't want to >> change it from slices to dynamic arrays, since the whole article is >> written around the subtle difference. I think the difference is important. >> >> -Steve >> >> [1] https://en.wikipedia.org/wiki/Dynamic_array > > I completely agree that the distinction between the dynamic array and the > memory that backs it is critical to understanding the semantics when copying > arrays around, and anyone who thinks that the dynamic array itself directly > controls and owns the memory is certainly going to have some problems > understanding the full semantics, but I don't agree that it's required to > talk about the underlying GC-allocated memory buffer as being the dynamic > array for that to be understood - especially when the dynamic array can be > backed with other memory to begin with and still have the same semantics > (just with a capacity of 0 and thus guaranteed reallocation upon appending > or calling reserve). That distinction can be made just fine using the > official D terminology. As soon as we call it "dynamic array", I can't help but think "adding elements". Since GC is in the picture when that happens, it's essential to think GC when adding an element is involved. Further, evident from your description it's a "slice" until you add elements because the underlying memory e.g. can be a stack-allocated fixed-length array. For these reasons, the interface that the program is using is a "slice". Dynamic array is a different concept owned and implemented by the GC. > I also don't agree that the way that D uses the term dynamic array > contradicts the wikipedia article. What it describes is very much how D's > dynamic arrays behave. It's just that D's dynamic arrays are a bit special > in that they let the GC manage the memory instead of encapsulating it all in > the type itself, and copying them slices the memory instead of copying it > and thus causing an immediate reallocation like you would get with > std::vector or treating it as a full-on reference type like Java does. But > the semantics of what happens when you append to a D dynamic array are the > same as appending to something like std::vector save for the fact that you > might end up having the capacity filled sooner, because another dynamic > array referring to the same memory grew into that space, resulting in a > reallocation - but std::vector would have reallocated as soon as you copied > it. So, some of the finer details get a bit confusing if you expect a > dynamic array to behave _exactly_ like std::vector, but at a high level, the > semantics are basically the same. You seem to anchor your view of array slices on appending elements to them. I see them mainly as accessors into existing elements. Add to that the fact that a slice does not have instruments itself to manage its memory, it remains a slice for me. Again, dynamic array is a GC thing that works behind the scenes. I can understand your point of view but I find it more confusing. > On the basis that you seem to be arguing that D's dynamic arrays aren't > really dynamic arrays, I could see someone arguing that std::vector isn't a > dynamic array, because unlike ArrayList, it isn't a reference type and thus > appending to the copy doesn't append to the original - or the other way > around; ArrayL
Re: Slices and Dynamic Arrays
On Tuesday, January 02, 2018 07:53:00 Steven Schveighoffer via Digitalmars- d-learn wrote: > On 1/1/18 12:18 AM, Jonathan M Davis wrote: > > A big problem with the term slice though is that it means more than just > > dynamic arrays - e.g. you slice a container to get a range over it, so > > that range is a slice of the container even though no arrays are > > involved at all. So, you really can't rely on the term slice meaning > > dynamic array. Whether it does or not depends on the context. That > > means that the fact that a number of folks have taken to using the term > > slice to mean T[] like the D Slices article talks about tends to create > > confusion when the context is not clear. IMHO, the D Slices article > > should be updated to use the correct terminology, but I don't think > > that the author is willing to do that. > The problem with all of this is that dynamic array is a defined term > *outside* of D [1]. And it doesn't mean exactly what D calls dynamic > arrays. > > This is why it's confusing to outsiders, because they are expecting the > same thing as a C++ std::vector, or a Java/.Net ArrayList, etc. And D > "array slices" (the proper term IMO) are not the same. > > I'm willing to change the article to mention "Array slices" instead of > just "slices", because that is a valid criticism. But I don't want to > change it from slices to dynamic arrays, since the whole article is > written around the subtle difference. I think the difference is important. > > -Steve > > [1] https://en.wikipedia.org/wiki/Dynamic_array I completely agree that the distinction between the dynamic array and the memory that backs it is critical to understanding the semantics when copying arrays around, and anyone who thinks that the dynamic array itself directly controls and owns the memory is certainly going to have some problems understanding the full semantics, but I don't agree that it's required to talk about the underlying GC-allocated memory buffer as being the dynamic array for that to be understood - especially when the dynamic array can be backed with other memory to begin with and still have the same semantics (just with a capacity of 0 and thus guaranteed reallocation upon appending or calling reserve). That distinction can be made just fine using the official D terminology. I also don't agree that the way that D uses the term dynamic array contradicts the wikipedia article. What it describes is very much how D's dynamic arrays behave. It's just that D's dynamic arrays are a bit special in that they let the GC manage the memory instead of encapsulating it all in the type itself, and copying them slices the memory instead of copying it and thus causing an immediate reallocation like you would get with std::vector or treating it as a full-on reference type like Java does. But the semantics of what happens when you append to a D dynamic array are the same as appending to something like std::vector save for the fact that you might end up having the capacity filled sooner, because another dynamic array referring to the same memory grew into that space, resulting in a reallocation - but std::vector would have reallocated as soon as you copied it. So, some of the finer details get a bit confusing if you expect a dynamic array to behave _exactly_ like std::vector, but at a high level, the semantics are basically the same. On the basis that you seem to be arguing that D's dynamic arrays aren't really dynamic arrays, I could see someone arguing that std::vector isn't a dynamic array, because unlike ArrayList, it isn't a reference type and thus appending to the copy doesn't append to the original - or the other way around; ArrayList isn't a dynamic array, because appending to a "copy" affects the original. The semantics of what happens when copying the array around are secondary to what being a dynamic array actually means, much as they obviously have a significant effect on how you write your code. The critical bits are how the memory is continguous and how appending is amortized to O(1). The semantics of copying clearly vary considerably depending on the exact implementation even if you ignore what D has done. I think that your article has been a great help, and the fact that you do a good job of describing the distinction between T[] and the memory behind it is critical. I just disagree with the terminology that you used when you did it, and I honestly think that the terminology used has a negative effect on understanding and dealing with dynamic arrays backed by non-GC-allocated memory, because the result seems to be that folks think that there's something different about them and how they behave (since they don't point to a "dynamic array" as your article uses the term), when in reality, there's really no difference in the semantics aside from the fact that their capacity is guaranteed to be 0 and thus reallocation is guaranteed upon appending or calling reserve, whereas for GC-backed dynamic arrays, capaci
Re: Slices and Dynamic Arrays
On 1/1/18 12:18 AM, Jonathan M Davis wrote: A big problem with the term slice though is that it means more than just dynamic arrays - e.g. you slice a container to get a range over it, so that range is a slice of the container even though no arrays are involved at all. So, you really can't rely on the term slice meaning dynamic array. Whether it does or not depends on the context. That means that the fact that a number of folks have taken to using the term slice to mean T[] like the D Slices article talks about tends to create confusion when the context is not clear. IMHO, the D Slices article should be updated to use the correct terminology, but I don't think that the author is willing to do that. The problem with all of this is that dynamic array is a defined term *outside* of D [1]. And it doesn't mean exactly what D calls dynamic arrays. This is why it's confusing to outsiders, because they are expecting the same thing as a C++ std::vector, or a Java/.Net ArrayList, etc. And D "array slices" (the proper term IMO) are not the same. I'm willing to change the article to mention "Array slices" instead of just "slices", because that is a valid criticism. But I don't want to change it from slices to dynamic arrays, since the whole article is written around the subtle difference. I think the difference is important. -Steve [1] https://en.wikipedia.org/wiki/Dynamic_array
Re: Slices and Dynamic Arrays
On Monday, 1 January 2018 at 02:10:14 UTC, Jonathan M Davis wrote: On Sunday, December 31, 2017 14:49:40 Tony via Digitalmars-d-learn wrote: On Sunday, 31 December 2017 at 14:24:40 UTC, Jonathan M Davis wrote: > [...] The DLang Tour also uses the term slice to refer to T[]. "The type of arr is int[], which is also called a slice." "A slice consists of two members - a pointer to the starting element and the length of the slice:" Presumably, because whoever wrote that preferred the terminology used in the D Slices article. Regardless, it's not wrong to call them slices. It's just less precise, since the term slice refers to more than dynamic arrays. The DLang Tour should probably be fixed to use the term dynamic array though. - Jonathan M Davis Editing a page is just one click away - there is an edit button on the top. Any improvements are always welcome!
Re: Slices and Dynamic Arrays
On Monday, January 01, 2018 05:06:46 Tony via Digitalmars-d-learn wrote: > On Monday, 1 January 2018 at 02:10:14 UTC, Jonathan M Davis wrote: > > The DLang Tour should probably be fixed to use the term dynamic > > array though. > > Or embrace both terms but take care that it is clear that they > are synonyms and one may be preferred depending on context. As a > beginner, I had some confusion seeing both terms used. > > There is dual terminology in use outside of dlang.org. The book > Programming In D says: > > Slice: Another name for dynamic array. > > When I write slice I will specifically mean a slice; and when I > write array, I will mean either a slice or a fixed-length array, > with no distinction. > > Slices > > Slices are the same feature as dynamic arrays. They are called > dynamic arrays for being used like arrays, and are called slices > for providing access to portions of other arrays. They allow > using those portions as if they are separate arrays. > --- A big problem with the term slice though is that it means more than just dynamic arrays - e.g. you slice a container to get a range over it, so that range is a slice of the container even though no arrays are involved at all. So, you really can't rely on the term slice meaning dynamic array. Whether it does or not depends on the context. That means that the fact that a number of folks have taken to using the term slice to mean T[] like the D Slices article talks about tends to create confusion when the context is not clear. IMHO, the D Slices article should be updated to use the correct terminology, but I don't think that the author is willing to do that. - Jonathan M Davis
Re: Slices and Dynamic Arrays
On Monday, 1 January 2018 at 02:10:14 UTC, Jonathan M Davis wrote: The DLang Tour should probably be fixed to use the term dynamic array though. Or embrace both terms but take care that it is clear that they are synonyms and one may be preferred depending on context. As a beginner, I had some confusion seeing both terms used. There is dual terminology in use outside of dlang.org. The book Programming In D says: Slice: Another name for dynamic array. When I write slice I will specifically mean a slice; and when I write array, I will mean either a slice or a fixed-length array, with no distinction. Slices Slices are the same feature as dynamic arrays. They are called dynamic arrays for being used like arrays, and are called slices for providing access to portions of other arrays. They allow using those portions as if they are separate arrays. ---
Re: Slices and Dynamic Arrays
On Sunday, December 31, 2017 14:49:40 Tony via Digitalmars-d-learn wrote: > On Sunday, 31 December 2017 at 14:24:40 UTC, Jonathan M Davis > > wrote: > > The D Slices article does an excellent job of explaining all of > > this. It's just that it calls the GC-allocated memory buffer > > the dynamic array instead of calling T[] the dynamic array like > > the language and spec do. Regardless, all non-null dynamic > > arrays are slices of memory. > > The DLang Tour also uses the term slice to refer to T[]. > > "The type of arr is int[], which is also called a slice." > > "A slice consists of two members - a pointer to the starting > element and the length of the slice:" Presumably, because whoever wrote that preferred the terminology used in the D Slices article. Regardless, it's not wrong to call them slices. It's just less precise, since the term slice refers to more than dynamic arrays. The DLang Tour should probably be fixed to use the term dynamic array though. - Jonathan M Davis
Re: Slices and Dynamic Arrays
On Sunday, 31 December 2017 at 14:24:40 UTC, Jonathan M Davis wrote: The D Slices article does an excellent job of explaining all of this. It's just that it calls the GC-allocated memory buffer the dynamic array instead of calling T[] the dynamic array like the language and spec do. Regardless, all non-null dynamic arrays are slices of memory. The DLang Tour also uses the term slice to refer to T[]. "The type of arr is int[], which is also called a slice." "A slice consists of two members - a pointer to the starting element and the length of the slice:"
Re: Slices and Dynamic Arrays
On Sunday, December 31, 2017 01:57:58 Tony via Digitalmars-d-learn wrote:
> On Friday, 29 December 2017 at 23:13:20 UTC, Jonathan M Davis
>
> wrote:
> > The term "slice" is a bit overused in D, meaning a variety of
> > things. It doesn't help that some folks dislike the official
> > terminology. In general, a slice is a contiguous group of
> > elements. A slice of memory would be a contiguous block of
> > memory. A dynamic array therefore refers to a slice of memory
> > and could be called a slice, but it's also the case that using
> > the slice operater on a container is called slicing - e.g.
> > rbt[] would give you a range over the container rbt, and that
> > range is a slice of the container, but it's not an array at all.
>
> 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. I would pick one or
> the other. It should be:
>
> D Arrays
>- Static
> - Dynamic
>
> or
>
> D Arrays
> - Static
> - Slice
>
>
> 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).
>
> D Arrays
> - Static
> - Dynamic
>- Slice-Initialized Dynamic
All dynamic arrays are slices of memory. What changes is what memory they're
sliced from. There is no master dynamic array that controls the memory that
backs all of these dynamic arrays. They're the same whether they were
allocated via new or slices from a static array or sliced from pointers or
whatever. _All_ a dynamic array is a pointer and a length - e.g.
struct DynamicArray(T)
{
size_t length;
T* ptr;
}
It has no mechanism for managing memory or tracking who owns it. All of that
is handled by whatever allocated the memory in the first place. In most
cases, that's the GC, but it doesn't have to be. The dynamic array doesn't
even have a way to keep track of its capacity. All of that is handled by the
GC.
Yes, appending to a dynamic array or calling reserve on it can cause memory
to be allocated by the GC, but that's because the GC looks at the capacity
of the array (which it calculates based on extra stuff it keeps track of)
and sees whether it can increase the length of the array in place (which it
can do only if the array is backed by GC-allocated memory, and the capacity
is greater than its current length). The GC then may allocate a new block of
memory and copy the contents of the array to the new memory, and the runtime
will adjust the two members of the dynamic array so that they point to the
new block of memory, but the dynamic array itself does none of this - and it
all works exactly the same if the dynamic array is backed by
non-GC-allocated memory. It's just that the GC will determine that since
it's not backed by GC-allocated memory, its capacity is 0, and any operation
that would need to increase the length or capacity of the array will need to
reallocate (after which, the dynamic array will be backed by GC-allocated
memory regardless of what backed it before).
In no case does the dynamic array itself manage its own memory, and there is
no concept of the "original" dynamic array that the others come from. As
confusing as that may seem at first, that simply isn't how dynamic arrays in
D work. Rather than being a container which you can get ranges over, they're
a weird hybrid between the two. They have operations that act like they own
and manage their own memory, but they really don't.
The D Slices article does an excellent job of explaining all of this. It's
just that it calls the GC-allocated memory buffer the dynamic array instead
of calling T[] the dynamic array like the language and spec do. Regardless,
all non-null dynamic arrays are slices of memory.
- Jonathan M Davis
Re: Slices and Dynamic Arrays
On Sunday, December 31, 2017 04:42:01 Tony via Digitalmars-d-learn wrote: > On Sunday, 31 December 2017 at 04:20:28 UTC, codephantom wrote: > > On Sunday, 31 December 2017 at 03:57:17 UTC, Tony wrote: > >> On Sunday, 31 December 2017 at 03:08:05 UTC, Ivan Trombley > >> > >> wrote: > >>> double[] D = [3.14159]; > >>> > >>> Can you guess what D is? :D > >> > >> It took me a while but I finally came up with "a slice of pi" > > > > a slice of pi is irrational. > > Even on special occasions? Of course. Cake is so much better. ;) - Jonathan M Davis
Re: Slices and Dynamic Arrays
On 12/30/17 10:08 PM, Ivan Trombley wrote: double[] D = [3.14159]; Can you guess what D is? :D An approximation of a slice of pi. -Steve
Re: Slices and Dynamic Arrays
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
Re: Slices and Dynamic Arrays
On Sunday, 31 December 2017 at 04:20:28 UTC, codephantom wrote: On Sunday, 31 December 2017 at 03:57:17 UTC, Tony wrote: On Sunday, 31 December 2017 at 03:08:05 UTC, Ivan Trombley wrote: double[] D = [3.14159]; Can you guess what D is? :D It took me a while but I finally came up with "a slice of pi" a slice of pi is irrational. Even on special occasions?
Re: Slices and Dynamic Arrays
On Sunday, 31 December 2017 at 03:57:17 UTC, Tony wrote: On Sunday, 31 December 2017 at 03:08:05 UTC, Ivan Trombley wrote: double[] D = [3.14159]; Can you guess what D is? :D It took me a while but I finally came up with "a slice of pi" a slice of pi is irrational.
Re: Slices and Dynamic Arrays
On Sunday, 31 December 2017 at 03:08:05 UTC, Ivan Trombley wrote: double[] D = [3.14159]; Can you guess what D is? :D It took me a while but I finally came up with "a slice of pi"
Re: Slices and Dynamic Arrays
double[] D = [3.14159]; Can you guess what D is? :D
Re: Slices and Dynamic Arrays
On Friday, 29 December 2017 at 23:13:20 UTC, Jonathan M Davis wrote: The term "slice" is a bit overused in D, meaning a variety of things. It doesn't help that some folks dislike the official terminology. In general, a slice is a contiguous group of elements. A slice of memory would be a contiguous block of memory. A dynamic array therefore refers to a slice of memory and could be called a slice, but it's also the case that using the slice operater on a container is called slicing - e.g. rbt[] would give you a range over the container rbt, and that range is a slice of the container, but it's not an array at all. 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. I would pick one or the other. It should be: D Arrays - Static - Dynamic or D Arrays - Static - Slice 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). D Arrays - Static - Dynamic - Slice-Initialized Dynamic
Re: Slices and Dynamic Arrays
On Friday, December 29, 2017 22:32:01 Tony via Digitalmars-d-learn wrote: > In DLang Tour:Arrays > https://tour.dlang.org/tour/en/basics/arrays > > there is: > --- > int size = 8; // run-time variable > int[] arr = new int[size]; > > The type of arr is int[], which is a slice. > --- > > In "D Slices" > https://dlang.org/d-array-article.html > > there is: > --- > int[] a; // a is a slice > > > Based on those two web pages it appears that the name for a > dynamic array in D is "slice". That is, anytime you > have a dynamic array (even a null reference version) it is called > a slice. Is that correct? No. The term "slice" is a bit overused in D, meaning a variety of things. It doesn't help that some folks dislike the official terminology. In general, a slice is a contiguous group of elements. A slice of memory would be a contiguous block of memory. A dynamic array therefore refers to a slice of memory and could be called a slice, but it's also the case that using the slice operater on a container is called slicing - e.g. rbt[] would give you a range over the container rbt, and that range is a slice of the container, but it's not an array at all. The "D Slices" article is great for explaining how things work but does not use the official terminology. Per the official terminology, T[] is a dynamic array regardless of what memory it refers to. Assuming that it's non-null, it _does_ refer to a slice of memory, and a number of folks follow the article and call T[] a slice and refer to the GC-allocated memory that a T[] usually refers to as the dynamic array, but officially, T[] is the dynamic array, and the memory it refers to has no special name. It's just a block of memory that is usually GC-allocated, but it could be malloced or be a slice of a static array or any other type of memory (since you can create a dynamic array from pointers), and its semantics don't change based on what type of memory backs it. I gather that the author chose to refer to the GC-allocated block of memory as the dynamic array because of how the term dynamic array is sometimes used elsewhere in computer science, but as far as D is concerned, T[] is a dynamic array regardless of what memory it refers to, and personally, I think that focusing on the GC-allocated memory block as being the dynamic array causes confusion when dealing with dynamic arrays that refer to non-GC-allocated memory, since the semantics are identical regardless of what memory backs the array (it's just that if the array does not refer to a slice of GC-allocated memory, the capacity is always 0, guaranteed that appending will reallocate instead of it just being a possibility), but too many folks tend to think of them as being different. A dynamic array that refers to non-GC-allocated memory is really the same thing as one that is GC-allocated except that when you slice non-GC-allocated memory to create a dynamic array, you then need to be aware of how to manage the lifetime of that memory so that no dynamic array refering to it outlives it (just like you'd have to do with a pointer to non-GC-allocated memory). But dynamic arrays never manage their own memory. It's just that the GC does the managing by default and will reallocate the memory backing a dynamic array if an operation can't be done in-place. - Jonathan M Davis
Re: Slices and Dynamic Arrays
On Friday, 29 December 2017 at 22:32:01 UTC, Tony wrote: In DLang Tour:Arrays https://tour.dlang.org/tour/en/basics/arrays there is: --- int size = 8; // run-time variable int[] arr = new int[size]; The type of arr is int[], which is a slice. --- In "D Slices" https://dlang.org/d-array-article.html there is: --- int[] a; // a is a slice Based on those two web pages it appears that the name for a dynamic array in D is "slice". That is, anytime you have a dynamic array (even a null reference version) it is called a slice. Is that correct? Not really, cause you can take a "slice" of a linked list (though inefficiently), but a linked list isn't an array. You can also take a "slice" of a stack allocated array.
Re: Slices and Dynamic Arrays
On Friday, 29 December 2017 at 22:32:01 UTC, Tony wrote: Based on those two web pages it appears that the name for a dynamic array in D is "slice". That is, anytime you have a dynamic array (even a null reference version) it is called a slice. Is that correct? Not exactly, but basically. read this for a bit more info https://dlang.org/d-array-article.html A slice is a bit more general than a dynamic array. You can slice into a static array, or any buffer really. The slice just also acts as a dynamic array and can create one on-demand if you append to it, and also slices are how D represents the underlying dynamic arrays to user code.
Slices and Dynamic Arrays
In DLang Tour:Arrays https://tour.dlang.org/tour/en/basics/arrays there is: --- int size = 8; // run-time variable int[] arr = new int[size]; The type of arr is int[], which is a slice. --- In "D Slices" https://dlang.org/d-array-article.html there is: --- int[] a; // a is a slice Based on those two web pages it appears that the name for a dynamic array in D is "slice". That is, anytime you have a dynamic array (even a null reference version) it is called a slice. Is that correct?
