Re: Calling assumeSorted on const(std.container.Array)
On Sunday, 26 March 2023 at 02:16:15 UTC, Steven Schveighoffer
wrote:
On 3/25/23 9:45 AM, Olivier Prat wrote:
[...]
It's because a Range keeps a copy of the array (Array is a
reference counted type). Since that is labeled `const`, then
editing the Range is forbidden.
Inside SortedRange, it has this, which is causing the issue:
```d
static if (isForwardRange!Range)
@property auto save()
{
// Avoid the constructor
typeof(this) result = this;
result._input = _input.save;
return result;
}
```
Overwriting the input isn't possible here, because it contains
a const member.
Now, this possibly could be fixed with something like:
`return typeof(this)(_input.save);`
But it might just push the error to another place.
The whole thing is kind of ugly.
There is a note inside the Array Range which says it's trying
to work around some old bug that is now marked as "works for
me", so maybe that can be reexamined.
https://github.com/dlang/phobos/blob/17b1a11afd74f9f8a69af93d77d4548a557e1b89/std/container/array.d#L137
-Steve
Thanks to both of you for the answers. It confirms my
investigation and my workaround is to cast the const ranges into
their non const versions, when I encounter these issues. Not very
pretty.
Re: Calling assumeSorted on const(std.container.Array)
On 3/25/23 9:45 AM, Olivier Prat wrote:
Would someone explain the exact nature of this error as I fail to
understand as how just telling that an Array ConstRange is assumed to be
sorted actually modifies anything??
It's because a Range keeps a copy of the array (Array is a reference
counted type). Since that is labeled `const`, then editing the Range is
forbidden.
Inside SortedRange, it has this, which is causing the issue:
```d
static if (isForwardRange!Range)
@property auto save()
{
// Avoid the constructor
typeof(this) result = this;
result._input = _input.save;
return result;
}
```
Overwriting the input isn't possible here, because it contains a const
member.
Now, this possibly could be fixed with something like:
`return typeof(this)(_input.save);`
But it might just push the error to another place.
The whole thing is kind of ugly.
There is a note inside the Array Range which says it's trying to work
around some old bug that is now marked as "works for me", so maybe that
can be reexamined.
https://github.com/dlang/phobos/blob/17b1a11afd74f9f8a69af93d77d4548a557e1b89/std/container/array.d#L137
-Steve
Re: Calling assumeSorted on const(std.container.Array)
On 3/25/23 09:31, Olivier Prat wrote: On Saturday, 25 March 2023 at 13:45:36 UTC, Olivier Prat wrote: I'm trying to call assumeSorted on a const(Array) using this code snippet: [...] In a similar fashion, a number of methods in SortedRange do not compile if called on a const(SortedRange) or immutable(SortedRange), such as length, or front. Is this on purpose? There are a number of interesting points in your original post but I couldn't find time to answer all of those. I can inject this for now: :) assumeSorted returns a range object. The concept of a const range object is flawed because by nature iteration of a range happens by mutating it: For example, popBack has to do that. So, it's normal that any range algorithm will assume a non-const object. Ali
Re: Calling assumeSorted on const(std.container.Array)
On Saturday, 25 March 2023 at 13:45:36 UTC, Olivier Prat wrote: I'm trying to call assumeSorted on a const(Array) using this code snippet: [...] In a similar fashion, a number of methods in SortedRange do not compile if called on a const(SortedRange) or immutable(SortedRange), such as length, or front. Is this on purpose?
Calling assumeSorted on const(std.container.Array)
I'm trying to call assumeSorted on a const(Array) using this code
snippet:
void test(T)(const ref Array!T a)
{
auto b = a[].assumeSorted;
writeln(b);
}
void main() {
Array!int a = [1, 5, 7, 8, 15, 100];
test(a);
}
Unfortunately, I keep having a compilation error:
/dlang/dmd/linux/bin64/../../src/phobos/std/range/package.d(10871): Error:
cannot modify struct instance `result._input` of type
`RangeT!(const(Array!int))` because it contains `const` or `immutable` members
/dlang/dmd/linux/bin64/../../src/phobos/std/range/package.d(10918): Error:
cannot modify struct instance `result._input` of type
`RangeT!(const(Array!int))` because it contains `const` or `immutable` members
/dlang/dmd/linux/bin64/../../src/phobos/std/range/package.d(11500): Error: template instance
`std.range.SortedRange!(RangeT!(const(Array!int)), "a < b",
SortedRangeOptions.assumeSorted)` error instantiating
onlineapp.d(10):instantiated from here: `assumeSorted!("a
< b", RangeT!(const(Array!int)))`
onlineapp.d(17):instantiated from here: `test!int`
Would someone explain the exact nature of this error as I fail to
understand as how just telling that an Array ConstRange is
assumed to be sorted actually modifies anything??
