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When will map/dict initialization be ready?
Apr 06, 2023
John Xu
Apr 06, 2023
Paul Backus
Apr 07, 2023
John Xu
April 06, 2023
Gravatar of John XuPosted by John XuReply
John Xu
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I saw on doc:
https://dlang.org/spec/hash-map.html#static_initialization,
that map/dict/associative array, still can't be initialized like below:

  NOTE: Not yet implemented.

  immutable long[string] aa = [
    "foo": 5,
    "bar": 10,
    "baz": 2000
  ];

I'm wondering when this is be ready? Python can write this way long time ago.

April 06, 2023
Gravatar of Paul BackusPosted by Paul Backus
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Paul Backus
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On Thursday, 6 April 2023 at 01:53:31 UTC, John Xu wrote:

>

I saw on doc:
https://dlang.org/spec/hash-map.html#static_initialization,
that map/dict/associative array, still can't be initialized like below:

  NOTE: Not yet implemented.

  immutable long[string] aa = [
    "foo": 5,
    "bar": 10,
    "baz": 2000
  ];

I'm wondering when this is be ready? Python can write this way long time ago.

Specifically, what doesn't work is initializing an associative array at compile time. You can use this syntax to initialize an AA at runtime, and it will work just fine.

For example:

// Error - global variables are initialized at compile time
long[string] globalAa = ["foo": 5, "bar": 10];

void main()
{
    // No error - local variables are initialized at runtime
    long[string] localAa = ["baz": 2000, "quux": 9999];
}

To work around this limitation, you can initialize a global AA using a static module constructor. For example:

long[string] globalAa;

static this()
{
    globalAa = ["foo": 5, "bar": 10];
}

This will perform the initialization at runtime, during program startup (before calling main).

April 06, 2023
Gravatar of Steven SchveighofferPosted by Steven Schveighoffer
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Steven Schveighoffer
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On 4/5/23 9:53 PM, John Xu wrote:
> I saw on doc:
>      https://dlang.org/spec/hash-map.html#static_initialization,
> that map/dict/associative array, still can't be initialized like below:
> 
>        NOTE: Not yet implemented.
> 
>        immutable long[string] aa = [
>          "foo": 5,
>          "bar": 10,
>          "baz": 2000
>        ];
> 
> I'm wondering when this is be ready? Python can write this way long time ago.

You can get almost the same thing via a library type that duplicates the layout of the runtime type. I did so in my `newaa` library:

https://code.dlang.org/packages/newaa

e.g.:

```d

immutable Hash!(long, string) aa = [
   "foo": 5,
   "bar": 10,
   "baz": 2000
];
```

The usage is a bit rough around the edges, I haven't implemented everything that is possible. But indexing works, should work for your use case.

But it can be cast to an AA using `asAA` (not sure about immutable support, I didn't test it too much).

-Steve
April 07, 2023
Gravatar of John XuPosted by John Xu
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John Xu
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On Thursday, 6 April 2023 at 02:49:55 UTC, Paul Backus wrote:

>

To work around this limitation, you can initialize a global AA using a [static module constructor][1]. For example:

long[string] globalAa;

static this()
{
    globalAa = ["foo": 5, "bar": 10];
}

This will perform the initialization at runtime, during program startup (before calling main).

Ok, great, thanks. Better add to the online document.