What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?

PS: I'm getting back to D after years (since DMD 1 days). A lot changes since v1.0.

On Wednesday, 21 February 2018 at 09:21:58 UTC, 0xFFFFFFFF wrote:
> What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?
>
> PS: I'm getting back to D after years (since DMD 1 days). A lot changes since v1.0.

Perhaps you are looking for slices: https://dlang.org/spec/arrays.html#slicing?

On 21/02/2018 9:21 AM, 0xFFFFFFFF wrote:
> What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?
> 
> PS: I'm getting back to D after years (since DMD 1 days). A lot changes since v1.0.

Think of string_view as a poor man's slice support.

Slices are essentially just dynamic arrays, a length and a pointer.

char* ptr = cast(char*)malloc(32);
char[] array = ptr[0 .. 32];

char[] anotherArray = array[16 .. $];
assert(anotherArray.length == 16);

It isn't limited to just char's either :)

On Wednesday, 21 February 2018 at 09:21:58 UTC, 0xFFFFFFFF wrote:
> What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?
>
> PS: I'm getting back to D after years (since DMD 1 days). A lot changes since v1.0.

Strings were always slices in D even in version 1.0, what's changed is that string data is immutable now - guaranteed to not change.

On Wednesday, February 21, 2018 09:21:58 0xFFFFFFFF via Digitalmars-d-learn wrote:
> What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?
>
> PS: I'm getting back to D after years (since DMD 1 days). A lot
> changes since v1.0.

strings in D are that way by their very nature, because they're dynamic arrays, and in D, dynamic arrays are just poiner and a length. Effectively, a dynamic array is

struct DynamicArray(T)
{
    size_t length;
    T* ptr;
}

They're slices of some piece of memory - usually GC-allocated memory, though you can slice any memory and get a dynamic array out of it. I'd suggest reading this article:

https://dlang.org/articles/d-array-article.html

It does not use the official terminology, because it refers to the GC-managed buffer as the dynamic array rather than the T[] as being the dynamic array (whereas the official terminology is that T[] is a dynamic array, regardless of what memory it's a slice of), but otherwise, what it says is quite good and should give you a solid idea of how arrays work in D.

- Jonathan M Davis

On Wednesday, 21 February 2018 at 09:21:58 UTC, 0xFFFFFFFF wrote:
> What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?
>
> PS: I'm getting back to D after years (since DMD 1 days). A lot changes since v1.0.

Wow! Thanks guys.
Those are handy, but I specifically want to do something like:

```
string_view sv = "some string";
```
So I can query it's size, make it point to sth else, use it in callbacks etc. Of course I'm aware of scoping etc...

I'm NOT doing any dynamic allocations, I just want a situation where a string allocation string would be a little bit expensive.


[I believe I still have to study D more in that case to come up with sth better, enjoying my ride so far]

On 21/02/2018 10:17 AM, 0xFFFFFFFF wrote:
> On Wednesday, 21 February 2018 at 09:21:58 UTC, 0xFFFFFFFF wrote:
>> What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?
>>
>> PS: I'm getting back to D after years (since DMD 1 days). A lot changes since v1.0.
> 
> Wow! Thanks guys.
> Those are handy, but I specifically want to do something like:
> 
> ```
> string_view sv = "some string";
> ```

string sv = "some string";
assert(sv.length == 11);

Or just "some string".length ;)

On Wednesday, February 21, 2018 10:17:55 0xFFFFFFFF via Digitalmars-d-learn wrote:
> On Wednesday, 21 February 2018 at 09:21:58 UTC, 0xFFFFFFFF wrote:
> > What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?
> >
> > PS: I'm getting back to D after years (since DMD 1 days). A lot
> > changes since v1.0.
>
> Wow! Thanks guys.
> Those are handy, but I specifically want to do something like:
>
> ```
> string_view sv = "some string";
> ```
> So I can query it's size, make it point to sth else, use it in
> callbacks etc. Of course I'm aware of scoping etc...
>
> I'm NOT doing any dynamic allocations, I just want a situation where a string allocation string would be a little bit expensive.
>
>
> [I believe I still have to study D more in that case to come up with sth better, enjoying my ride so far]

As I said in my previous response, read this article:

https://dlang.org/articles/d-array-article.html

You clearly do not understand at all how strings work in D. Strings in D basically _are_ string_views where most strings have the actual memory buffer managed by the GC. If you do

string sv = "some string";

then _zero_ heap allocations take place.

- Jonathan M Davis

0xFFFFFFFF wrote:

> On Wednesday, 21 February 2018 at 09:21:58 UTC, 0xFFFFFFFF wrote:
>> What is the equivalent of C++17 std::string_view (an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero) in D?
>>
>> PS: I'm getting back to D after years (since DMD 1 days). A lot changes since v1.0.
>
> Wow! Thanks guys.
> Those are handy, but I specifically want to do something like:
>
> ```
> string_view sv = "some string";
> ```
> So I can query it's size, make it point to sth else, use it in callbacks etc. Of course I'm aware of scoping etc...
>
> I'm NOT doing any dynamic allocations, I just want a situation where a string allocation string would be a little bit expensive.

and that is exactly what slices are for! ;-)

you are probably better to use `const(char)[]`, tho. like this:

	// don't store `s`, as it's contents may change after exiting of `myfunc`
	// (this is what `const` implies here)
	void myfunc (const(char)[] s) { ... }

	...
	string s = "test string";
	myfunc(s); // yep, this works
	s = s[2..4]; // this doesn't allocate
	myfunc(s);
	myfunc(s[3..6]); // or this, it doesn't allocate
	myfunc("abc"); // or this, doesn't allocate

you got the idea.

On Wednesday, 21 February 2018 at 10:23:23 UTC, Jonathan M Davis wrote:
> As I said in my previous response, read this article:
>
> https://dlang.org/articles/d-array-article.html

Sorry, I didn't see this before I replied.
Had I, I wouldn't have done that.

>string sv = "some string";
>then _zero_ heap allocations take place.

I think u've answered my question.