length field of a const SortedRange

[dlangBugzillaToGithub]

bearophile_hugs reported this on 2013-03-23T07:50:35Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=9792

CC List

• acehreli
• justin
• n8sh.secondary
• peter.alexander.au (@Poita)
• witold.baryluk+d (@baryluk)

Description

I'd like this code to work:


import std.algorithm: sort;
void main() {
    const data = [1, 5, 2].sort();
    auto len = data.length;
}


DMD 2.063alpha gives:

temp.d(4): Error: mutable method std.range.SortedRange!(int[], "a < b").SortedRange.length is not callable using a const object

[dlangBugzillaToGithub]

justin commented on 2014-02-03T16:25:48Z

(In reply to comment #0)
> I'd like this code to work:
> 
> 
> import std.algorithm: sort;
> void main() {
>     const data = [1, 5, 2].sort();
>     auto len = data.length;
> }
> 
> 
> DMD 2.063alpha gives:
> 
> temp.d(4): Error: mutable method std.range.SortedRange!(int[], "a <
> b").SortedRange.length is not callable using a const object

Additionally `contains`, and probably `lowerBound`, `equalRange`, and `upperBound`.

[dlangBugzillaToGithub]

peter.alexander.au (@Poita) commented on 2014-02-07T13:31:03Z

This is easy to fix in the library, but we'd need special code to handle it correctly, which would need to be duplicated for every function.

Once Issue 7521 is implemented, it will be solved automatically (the const will be inferred, when possible).

[dlangBugzillaToGithub]

acehreli commented on 2020-02-26T23:00:06Z

I ran into this in a post condition code:

import std.algorithm;

auto foo()
out (result; result.length == 1) { // <-- ERROR
  return [ 0 ].sort;
}

void main() {
}

Error: mutable method `std.range.SortedRange!(int[], "a < b").SortedRange.length` is not callable using a `const` object
Consider adding `const` or `inout` to std.range.SortedRange!(int[], "a < b").SortedRange.length

Ali

[dlangBugzillaToGithub]

witold.baryluk+d (@baryluk) commented on 2020-04-30T13:46:20Z

I got similar issues with constness, in other cirumstances. `opIndex` and `opSlice` could be made const too, if they return const range or SortedRange, and underlying Range is const.

I have a method like this:

void search(Range, T)(in T[] needles, in SortedRange!(Range) haystack, long[] ret, const long index_offset) {

it is called as search(needles, assumeSorted(kaystack), ret, 0);


but the body of this function does pose issues:

search.d:67:7: error: mutable method std.range.SortedRange!(const(int)[], "a < b").SortedRange.length is not callable using a const object
   67 |   if (haystack.length == 0) {
      |       ^
search.d:83:17: error: mutable method std.range.SortedRange!(const(int)[], "a < b").SortedRange.opIndex is not callable using a const object
   83 |     if (haystack[i] == needles[j]) {


This is with gdc 9.3.0-11 and libgphobos76 9.3.0-11.



It looks like automatic inference of const methods, or specialization of const and non-const (at the cost of repeating the same code twice) is required to make it work.

[dlangBugzillaToGithub]

witold.baryluk+d (@baryluk) commented on 2020-04-30T14:27:00Z

Same issue with `SortedRange.trisect` too.