Type-Safe template wrapper for AA

[marler8997]

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[wilzbach]

Nice. I was about to add this too, but you beat me to it :)

[wilzbach]

How about adding opIndexAssign too?

    auto opIndexAssign(V value, K key)
    {
        auto ptr = dmd_aaGet(&aa, cast(void*) key);
        *ptr = cast(void*) value;
        return *ptr;
    }

[marler8997]

Currently no code uses it this way and I don't anticipate code ever doing this.

aa[key] = value;

This being the more "intuitive" usage, I have to assume that Walter deliberately chose not to support this.

[timotheecour]

maybe it's just because it wasn't implemented? maybe ask @WalterBright ?

[marler8997]

I don't think it's something worth bugging him about. Currently there's no use for it. We can always add it later if a use comes to light.

[JinShil]

Keep in mind that the current code base was translated from C+ (not a typo). I don't think there was any deliberate effort by Walter to avoid it.

[marler8997]

I'm also basing this on comments he made about one of @ibuclaw's PRs where he made a change that ended up causing multiple lookups of the same key. The current implementation uses getLvalue which allows the developer to do multiple operations on a value with only one lookup. I think the Walter designed the API to encourage this behavior, and adding opIndexAssign would provide a way to circumvent it, making it easy for developers to accidentally write code that performs multiple lookups that aren't necessary.

[marler8997]

Here's Walter's comment: #7696 (comment)

[wilzbach]

How about adding a public example:

///
unittest
{
    AssocArray!(string, int) aa;

    assert(aa["foo"] == 0);
    aa["foo"] = 2;
    assert(aa["foo"] == 2);
    assert(aa.length == 1);
}

[wilzbach]

Nice. I added this to the "no objection -> merge" queue.

[nordlow]

Whats the purpose with this addition?

[marler8997]

I thought the purpose was self evident from the change (and the title)...what do you think?

[nordlow]

1. Is the long-term goal with this change to make the default AA-implementation user-configurable?
2. Without the reading the code...what kinds of extra type-safety does this change introduce?

[marler8997]

No long term goal in mind for this change, the change is its own end goal, a type safe template wrapper around AA.

[wilzbach]

This has nothing to do with druntime. It's about introducing more type safety into the dmd codebase which uses its own AA-implementation back from the C++ times.

I think what you are looking for is something like dlang/druntime#1282

[nordlow]

Ahh, now I get it. Thanks, @wilzbach, I thought I was looking at a druntime PR... my mistake.