AA initialization
Kozzi11 via Digitalmars-d-learn
digitalmars-d-learn at puremagic.com
Wed Aug 6 06:15:26 PDT 2014
On Wednesday, 6 August 2014 at 11:32:41 UTC, Puming wrote:
> I found AA initialization have a strange effect:
>
> ```d
> string[string] map; // same as `string[string] map =
> string[string].init;
> writeln(map); // output: []
>
> string[string] refer = map; // make a reference
> refer["1"] = "2"; // update the reference
> writeln(map); // output: []. The reference does not affect the
> original.
> ```
>
> But if I do an assignment first, the reference works:
>
>
> ```d
> string[string] map; // same as `string[string] map =
> string[string].init;
> writeln(map); // output: []
>
> map["1"] = "0";
>
> string[string] refer = map; // make a reference
> refer["1"] = "2"; // update the reference
> writeln(map); // output: ["1":"2"]. The reference does affect.
> ```
>
> So if I want an empty AA and want to use a variable to refer to
> it later, I have to do this:
>
> ```d
> string[string] map; // same as `string[string] map =
> string[string].init;
>
> map["1"] = "0";
> map.remove("1"); // assign and then REMOVE!
> writeln(map); // output: []
>
> string[string] refer = map; // make a reference
> refer["1"] = "2"; // update the reference
> writeln(map); // output: ["1":"2"]. The reference does affect.
> ```
>
> which looks awkward.
>
> Is it because `string[string].init == null` ? If so, how do I
> specify an empty AA which is not null? Neither `[]` or `[:]`
> seems to work.
AFAIK there is no easy way to do it. Maybe it would be fine to
add some function to phobos. Something like this:
auto initAA(VT,KT)() {
static struct Entry
{
Entry *next;
size_t hash;
}
static struct Impl
{
Entry*[] buckets;
size_t nodes;
TypeInfo _keyti;
Entry*[4] binit;
@property const(TypeInfo) keyti() const @safe pure nothrow @nogc
{ return _keyti; }
}
static struct AA
{
Impl* impl;
}
VT[KT] aaa;
AA* aa = cast(AA*)&aaa;
if (aa.impl is null)
{ aa.impl = new Impl();
aa.impl.buckets = aa.impl.binit[];
}
aa.impl._keyti = cast() typeid(aaa);
return aaa;
}
Or it would be fine if I could write something like this: auto aa
= new VT[KT]();
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