• Elronnd (5/5) Jul 29 2021 const(int)[int] d;
• Tejas (3/8) Aug 04 2021 Casting ```const``` away is undefined behaviour in D. And what is
• jfondren (18/27) Aug 04 2021 what's wanted here is an assign-once hash table, I imagine.
• Tejas (14/42) Aug 04 2021 Well, OP will have to create non-const AA first and then cast it
• Mathias LANG (4/9) Aug 04 2021 You aren't missing anything. It's a bug, and should be fixed, but

Elronnd <elronnd elronnd.net> writes:

const(int)[int] d;
d.require(5, 7); //compile error

 From a semantics perspective, though, I don't think there's 
anything wrong with this, and 'require' could reasonably cast the 
const away before assigning.  Am I missing anything?

Tejas <notrealemail gmail.com> writes:

On Thursday, 29 July 2021 at 20:44:35 UTC, Elronnd wrote:
 const(int)[int] d;
 d.require(5, 7); //compile error

 From a semantics perspective, though, I don't think there's 
 anything wrong with this, and 'require' could reasonably cast 
 the const away before assigning.  Am I missing anything?

Casting ```const``` away is undefined behaviour in D. And what is 
this "require"? Maybe show more code?

jfondren <julian.fondren gmail.com> writes:

On Wednesday, 4 August 2021 at 08:08:35 UTC, Tejas wrote:
 On Thursday, 29 July 2021 at 20:44:35 UTC, Elronnd wrote:
 const(int)[int] d;
 d.require(5, 7); //compile error

 From a semantics perspective, though, I don't think there's 
 anything wrong with this, and 'require' could reasonably cast 
 the const away before assigning.  Am I missing anything?

 Casting ```const``` away is undefined behaviour in D. And what 
 is this "require"? Maybe show more code?

what's wanted here is an assign-once hash table, I imagine.

require is https://dlang.org/phobos/object.html#.require , and 
it'd be the assignment line of that code that would have to cast 
away const.

```d
unittest {
     int[int] nums;
     nums.require(0, 0);
     nums[0]++;
     assert(nums == [0: 1]);
}

unittest {
     const(int)[int] nums;
     assert(__traits(compiles, nums.require(0, 0)));
     assert(!__traits(compiles, nums[0]++));
}
```

Tejas <notrealemail gmail.com> writes:

On Wednesday, 4 August 2021 at 09:43:57 UTC, jfondren wrote:
 On Wednesday, 4 August 2021 at 08:08:35 UTC, Tejas wrote:
 On Thursday, 29 July 2021 at 20:44:35 UTC, Elronnd wrote:
 const(int)[int] d;
 d.require(5, 7); //compile error

 From a semantics perspective, though, I don't think there's 
 anything wrong with this, and 'require' could reasonably cast 
 the const away before assigning.  Am I missing anything?

 Casting ```const``` away is undefined behaviour in D. And what 
 is this "require"? Maybe show more code?

 what's wanted here is an assign-once hash table, I imagine.

 require is https://dlang.org/phobos/object.html#.require , and 
 it'd be the assignment line of that code that would have to 
 cast away const.

 ```d
 unittest {
     int[int] nums;
     nums.require(0, 0);
     nums[0]++;
     assert(nums == [0: 1]);
 }

 unittest {
     const(int)[int] nums;
     assert(__traits(compiles, nums.require(0, 0)));
     assert(!__traits(compiles, nums[0]++));
 }
 ```

Well, OP will have to create non-const AA first and then cast it 
to const, it seems.

```d
import std;
void main()
{
     int[int] a;
     a.require(5,7);
     auto b = cast(const(int)[int])a;
}

```

Probably hide the process behind a function to make it look more 
smooth; otherwise I'm outta ideas.

Mathias LANG <geod24 gmail.com> writes:

On Thursday, 29 July 2021 at 20:44:35 UTC, Elronnd wrote:
 const(int)[int] d;
 d.require(5, 7); //compile error

 From a semantics perspective, though, I don't think there's 
 anything wrong with this, and 'require' could reasonably cast 
 the const away before assigning.  Am I missing anything?

You aren't missing anything. It's a bug, and should be fixed, but 
that'll require making the frontend understand what `require` is 
(or providing a way to express this in a generic manner).