Re: Whats the proper way to write a Range next function
On 2022-06-15 19:36, JG wrote:
On Wednesday, 15 June 2022 at 17:30:31 UTC, JG wrote:
On Wednesday, 15 June 2022 at 13:52:24 UTC, Christian Köstlin wrote:
the naive version would look like
```d
auto next(Range)(Range r) {
r.popFront;
return r.front;
}
```
But looking at a mature library e.g.
https://github.com/submada/btl/blob/9cc599fd8495215d346ccd62d6e9f1f7ac140937/source/btl/vector/package.d#L229
is looks like there should be tons of annotations/attributes on it.
Kind regards,
Christian
I not sure of your use case. But you need to check if the range is
empty before and after calling popFront (and decide what to if it is).
Also unless you want the original range passed in mutated you should
call save (assuming you have a forward range) before calling your next
or you need to modify next so it calls save.
This is what I would write for next (which should only be called after
checking if the range is empty).
It produces a range whose front points at the next element.
```d
auto next(Range)(Range r) {
auto ret = r.save;
ret.popFront;
return ret;
}
```
Thanks for the explanation!
I actually want to mutate the original range and I know, that there are
at least 2 elements in my range.
e.g. the program
```d
import std.stdio;
import std.range;
auto next(Range)(Range r) {
r.popFront;
return r.front;
}
int main(string[] args) {
auto i = iota(10);
writeln(i.next);
writeln(i.next);
return 0;
}
```
prints:
```
1
1
```
whereas
```d
import std.stdio;
import std.range;
auto next(Range)(ref Range r) {
r.popFront;
return r.front;
}
int main(string[] args) {
auto i = iota(10);
writeln(i.next);
writeln(i.next);
return 0;
}
```
prints
```
1
2
```
which is what I would want. So it depends if the Range is a value or
reference type ...
Re: Whats the proper way to write a Range next function
On Wednesday, 15 June 2022 at 17:30:31 UTC, JG wrote:
On Wednesday, 15 June 2022 at 13:52:24 UTC, Christian Köstlin
wrote:
the naive version would look like
```d
auto next(Range)(Range r) {
r.popFront;
return r.front;
}
```
But looking at a mature library e.g.
https://github.com/submada/btl/blob/9cc599fd8495215d346ccd62d6e9f1f7ac140937/source/btl/vector/package.d#L229 is looks like there should be tons of annotations/attributes on it.
Kind regards,
Christian
I not sure of your use case. But you need to check if the range
is empty before and after calling popFront (and decide what to
if it is). Also unless you want the original range passed in
mutated you should call save (assuming you have a forward
range) before calling your next or you need to modify next so
it calls save.
This is what I would write for next (which should only be called
after
checking if the range is empty).
It produces a range whose front points at the next element.
```d
auto next(Range)(Range r) {
auto ret = r.save;
ret.popFront;
return ret;
}
```
Re: Whats the proper way to write a Range next function
On Wednesday, 15 June 2022 at 13:52:24 UTC, Christian Köstlin
wrote:
the naive version would look like
```d
auto next(Range)(Range r) {
r.popFront;
return r.front;
}
```
But looking at a mature library e.g.
https://github.com/submada/btl/blob/9cc599fd8495215d346ccd62d6e9f1f7ac140937/source/btl/vector/package.d#L229 is looks like there should be tons of annotations/attributes on it.
Kind regards,
Christian
I not sure of your use case. But you need to check if the range
is empty before and after calling popFront (and decide what to if
it is). Also unless you want the original range passed in mutated
you should call save (assuming you have a forward range) before
calling your next or you need to modify next so it calls save.
Re: Whats the proper way to write a Range next function
On Wednesday, 15 June 2022 at 13:52:24 UTC, Christian Köstlin wrote: looks like there should be tons of annotations/attributes on it. Because you have a template function, most attributes will be inferred based on the Range type. `const` is not inferred, but `popFront` mutates so it doesn't apply in your case. `@property` is not inferred either, but the spec says "Using property functions is not recommended until the definition is more certain and implementation more mature."
Whats the proper way to write a Range next function
the naive version would look like
```d
auto next(Range)(Range r) {
r.popFront;
return r.front;
}
```
But looking at a mature library e.g.
https://github.com/submada/btl/blob/9cc599fd8495215d346ccd62d6e9f1f7ac140937/source/btl/vector/package.d#L229
is looks like there should be tons of annotations/attributes on it.
Kind regards,
Christian
