Re: How to make AA key a pointer

[Clinton via Digitalmars-d-learn]

On Monday, 19 February 2018 at 15:02:29 UTC, ketmar wrote:

Clinton wrote:


On Monday, 19 February 2018 at 14:55:01 UTC, Clinton wrote:

[...]


Sorry, on second look my explanation isn't very clear. I want 
to know if:


bool[string] myAA;

myAA[contact.id] = true; // Does this copy contact.id or is 
this a pointer to contact.id?


there is absolutely no reason to copy `string` ever, as it is 
`immutable`. and compiler knows that. anyway, why don't you 
just check it by writing the code first?


import std.stdio;
void main () {
int[string] a;
string s = "test";
writefln("%08x", s.ptr);
a[s] = 666;
s = "test1";
writefln("%08x", s.ptr);
a[s] = 42;
foreach (string k; a.byKey) writefln("%08x", k.ptr);
}


Thanks. I actually did a similar test a little while ago and 
found it out. Thanks for confirming. I still struggle a bit with 
these basic things.

Re: How to make AA key a pointer

[ketmar via Digitalmars-d-learn]

Clinton wrote:


On Monday, 19 February 2018 at 14:55:01 UTC, Clinton wrote:

Hi all, I need advice from better developers on this concern.

I'm using an AA to reference another array for quicker access:

[...]


Sorry, on second look my explanation isn't very clear. I want to know if:

bool[string] myAA;

myAA[contact.id] = true; // Does this copy contact.id or is this a 
pointer to contact.id?


there is absolutely no reason to copy `string` ever, as it is `immutable`. 
and compiler knows that. anyway, why don't you just check it by writing the 
code first?


import std.stdio;
void main () {
int[string] a;
string s = "test";
writefln("%08x", s.ptr);
a[s] = 666;
s = "test1";
writefln("%08x", s.ptr);
a[s] = 42;
foreach (string k; a.byKey) writefln("%08x", k.ptr);
}

Re: How to make AA key a pointer

[Rene Zwanenburg via Digitalmars-d-learn]

On Monday, 19 February 2018 at 14:57:47 UTC, Clinton wrote:

On Monday, 19 February 2018 at 14:55:01 UTC, Clinton wrote:

Hi all, I need advice from better developers on this concern.

I'm using an AA to reference another array for quicker access:

[...]


Sorry, on second look my explanation isn't very clear. I want 
to know if:


bool[string] myAA;

myAA[contact.id] = true; // Does this copy contact.id or is 
this a pointer to contact.id?


It's a pointer. In D, string is an alias to immutable(char)[] 
(Slice of immutable characters). A slice is a combination of 
pointer and length.

Re: How to make AA key a pointer

[Clinton via Digitalmars-d-learn]

On Monday, 19 February 2018 at 14:55:01 UTC, Clinton wrote:

Hi all, I need advice from better developers on this concern.

I'm using an AA to reference another array for quicker access:

[...]


Sorry, on second look my explanation isn't very clear. I want to 
know if:


bool[string] myAA;

myAA[contact.id] = true; // Does this copy contact.id or is this 
a pointer to contact.id?

How to make AA key a pointer

[Clinton via Digitalmars-d-learn]

Hi all, I need advice from better developers on this concern.

I'm using an AA to reference another array for quicker access:

[code]
alias contactId = string;
bool[contactId][] matches;
ulong[contactId] idsToMatches;

bool[string] matchesForId(string id) {
  return matches.get(idsToMatches[id], bool[string].init);
}
[/code]

Just wondering, how do I set the keys to avoid copying the id 
string? So, let's say ids come from another array of structs(e.g. 
Contact[]). I want to avoid having two copies of the string id 
value in both of these AAs above (to avoid using extra memory 
usage).


The reason this is a potential issue is because these arrays can 
get extremely large. This is to match duplicate contacts and 
group them in matches. The reason I use bool is because it's the 
smallest size type and I don't think I can use void.


I guess my question is: does dmd already create pointers to the 
id from the AA, or is each new key a new allocation?