assocArray famously complains that it needs a mutable value type. You can't set values. You could write a literal, but that only works for a finite number of keys, and there's no way to merge two associative arrays.

Internally, we use librebindable, so we can create a Rebindable!(immutable V)[K], which is mutable, and cast it to immutable V[K] without breaking anything. But I'm not sure how I'd propose getting that into Phobos without including librebindable outright. But I also don't see another way to do it?

Any ideas?

On 10/7/22 2:58 AM, FeepingCreature wrote:

require should work, since it effectively only assigns a value if it doesn't already exist.

If it doesn't, then maybe it can be fixed so it does.

We can't allow just general assignment to compile, as you may have an already existing value.

-Steve

On Friday, 7 October 2022 at 13:58:52 UTC, Steven Schveighoffer wrote:

Can confirm that require doesn't work at present:

void main() {
    immutable(int)[int] aa;
    aa.require(5, 5);
    assert(aa[5] == 5);
}

/dlang/dmd/linux/bin64/../../src/druntime/import/object.d(3453): Error: cannot modify immutable expression *p
onlineapp.d(5): Error: template instance object.require!(int, immutable(int)) error
instantiating

It's hard to see how you'd make require work but not assocArray, since require is not exactly a built-in feature either.

On 10/7/22 11:27 AM, FeepingCreature wrote:

You can either cast (which is reasonable, considering that the assignment only happens when it didn't already exist) or make a new hook.

-Steve

On Friday, 7 October 2022 at 16:03:49 UTC, Steven Schveighoffer wrote:

cast is not sufficient because immutable struct S cannot by any means be made mutable.

On 10/7/22 12:11 PM, FeepingCreature wrote:

copyEmplace appears to work:

import core.lifetime;
immutable struct S
{
    int x;
}
void main()
{
    S s = S(5);
    ubyte[S.sizeof] buf;
    copyEmplace(s, *cast(S*)buf.ptr);
}

-Steve

On Friday, 7 October 2022 at 18:00:56 UTC, Steven Schveighoffer wrote:

import core.lifetime;
immutable struct S
{
    int x;
}
void main()
{
    S s = S(5);
    ubyte[S.sizeof] buf;
    copyEmplace(s, *cast(S*)buf.ptr);
}

Yeah, if I could get the associative array to give me a pointer to an uninitialized value for a key, that would do it, I think.

On 10/7/22 3:20 PM, FeepingCreature wrote:

Have you looked at the implementation for require? That's exactly what it does.

For reference: https://github.com/dlang/dmd/blob/f4c21ccd6a73fee7abdea39cc38e8c64b627ffe1/druntime/src/object.d#L3457

-Steve

On Friday, 7 October 2022 at 20:04:48 UTC, Steven Schveighoffer wrote:

Yeah okay so it's definitely possible, but I do feel it's kinda questionable to call barely documented internal implementation-dependent (?) runtime functions from user code...

On Saturday, 8 October 2022 at 17:09:39 UTC, FeepingCreature wrote:

What's missing from the docs?
Besides object there's also the AA docs:
https://dlang.org/spec/hash-map.html#inserting_if_not_present