The following

string[string] myarray = ["key":"value"];
string entry;
entry = myarray["key"]; // => vgc: indexing an associative array may cause GC allocation

Why is _accessing_ an assoc treated as indexing it?

On Mon, 18 May 2015 14:30:42 +0000, Chris wrote:

> The following
> 
> string[string] myarray = ["key":"value"];
> string entry;
> entry = myarray["key"]; // => vgc: indexing an associative array may
> cause GC allocation
> 
> Why is _accessing_ an assoc treated as indexing it?

it can throw "out of range" error, which is `new`ed.

On Monday, 18 May 2015 at 14:34:38 UTC, ketmar wrote:
> On Mon, 18 May 2015 14:30:42 +0000, Chris wrote:
>
>> The following
>> 
>> string[string] myarray = ["key":"value"];
>> string entry;
>> entry = myarray["key"]; // => vgc: indexing an associative array may
>> cause GC allocation
>> 
>> Why is _accessing_ an assoc treated as indexing it?
>
> it can throw "out of range" error, which is `new`ed.

But shouldn't it read "accessing an associative array may cause GC allocation"? And maybe a hint to the exception that may be thrown.

It's not the same as

myarray["key1] = "some value";
myarray["key2] = "some other value";

A bit confusing.

On Mon, 18 May 2015 14:41:19 +0000, Chris wrote:

> On Monday, 18 May 2015 at 14:34:38 UTC, ketmar wrote:
>> On Mon, 18 May 2015 14:30:42 +0000, Chris wrote:
>>
>>> The following
>>> 
>>> string[string] myarray = ["key":"value"];
>>> string entry;
>>> entry = myarray["key"]; // => vgc: indexing an associative array may
>>> cause GC allocation
>>> 
>>> Why is _accessing_ an assoc treated as indexing it?
>>
>> it can throw "out of range" error, which is `new`ed.
> 
> But shouldn't it read "accessing an associative array may cause GC allocation"?

not any access may cause allocation. `auto e = "key" in myarray;` will not allocate, for example. yet it's still accessing the array. it's *indexing* which may end in allocation.

> And maybe a hint to the exception that may be thrown.
i believe that such explanation is a work for lint-like tool. burden compiler with special cases can lead too far. ;-)

> It's not the same as
> 
> myarray["key1] = "some value";
> myarray["key2] = "some other value";
> 
> A bit confusing.

yes, it requires some knowledge of language and libraries. "-vgc" is not a linter, though, it was made with some assumptions about user's knowledge.

yet you can open ER in bugzilla, maybe DMD developers will implement it. i'm not a developer, and i can be wrong in reasons behind "-vgc".

On Monday, 18 May 2015 at 18:40:15 UTC, ketmar wrote:
> On Mon, 18 May 2015 14:41:19 +0000, Chris wrote:
>
>> On Monday, 18 May 2015 at 14:34:38 UTC, ketmar wrote:
>>> On Mon, 18 May 2015 14:30:42 +0000, Chris wrote:
>>>
>>>> The following
>>>> 
>>>> string[string] myarray = ["key":"value"];
>>>> string entry;
>>>> entry = myarray["key"]; // => vgc: indexing an associative array may
>>>> cause GC allocation
>>>> 
>>>> Why is _accessing_ an assoc treated as indexing it?
>>>
>>> it can throw "out of range" error, which is `new`ed.
>> 
>> But shouldn't it read "accessing an associative array may cause GC
>> allocation"?
>
> not any access may cause allocation. `auto e = "key" in myarray;` will
> not allocate, for example. yet it's still accessing the array. it's
> *indexing* which may end in allocation.

Yes, that's exactly what was driving at. Accessing is not indexing, and yet I get a warning for _indexing_, while the real reason is that a wrong access can cause an exception (which allocates). I.e. it should be

"accessing an associative array may cause GC allocation on error"

Maybe the message with "indexing" for accessing is merely reusing the message for indexing, or all assoc array operations are lumped together as "indexing". I dunno. It seems wrong to me, because it's inaccurate.

>> And maybe a hint to the exception that may be thrown.
> i believe that such explanation is a work for lint-like tool. burden
> compiler with special cases can lead too far. ;-)
>
>> It's not the same as
>> 
>> myarray["key1] = "some value";
>> myarray["key2] = "some other value";
>> 
>> A bit confusing.
>
> yes, it requires some knowledge of language and libraries. "-vgc" is not
> a linter, though, it was made with some assumptions about user's
> knowledge.
>
> yet you can open ER in bugzilla, maybe DMD developers will implement it.
> i'm not a developer, and i can be wrong in reasons behind "-vgc".

On Monday, 18 May 2015 at 14:30:43 UTC, Chris wrote:
> The following
>
> string[string] myarray = ["key":"value"];
> string entry;
> entry = myarray["key"]; // => vgc: indexing an associative array may cause GC allocation
>
> Why is _accessing_ an assoc treated as indexing it?

No error if you use myarray.get("key", null); or string* entry = "key" in myarray;

On Tuesday, 19 May 2015 at 09:10:50 UTC, Namespace wrote:
> On Monday, 18 May 2015 at 14:30:43 UTC, Chris wrote:
>> The following
>>
>> string[string] myarray = ["key":"value"];
>> string entry;
>> entry = myarray["key"]; // => vgc: indexing an associative array may cause GC allocation
>>
>> Why is _accessing_ an assoc treated as indexing it?
>
> No error if you use myarray.get("key", null); or string* entry = "key" in myarray;

What are the advantages / disadvantages of the two methods?

On Monday, 18 May 2015 at 14:30:43 UTC, Chris wrote:

> Why is _accessing_ an assoc treated as indexing it?

Are you sure you understand "indexing" as we do? It's not like indexing of databases, it's just "accessing by index" i.e. using myarray[some_index].

On Tuesday, 19 May 2015 at 09:43:06 UTC, Chris wrote:
> On Tuesday, 19 May 2015 at 09:10:50 UTC, Namespace wrote:
>> On Monday, 18 May 2015 at 14:30:43 UTC, Chris wrote:
>>> The following
>>>
>>> string[string] myarray = ["key":"value"];
>>> string entry;
>>> entry = myarray["key"]; // => vgc: indexing an associative array may cause GC allocation
>>>
>>> Why is _accessing_ an assoc treated as indexing it?
>>
>> No error if you use myarray.get("key", null); or string* entry = "key" in myarray;
>
> What are the advantages / disadvantages of the two methods?

You could get null with "in" if your key is not there. Besides that, no disadvantages.

On Tuesday, 19 May 2015 at 11:08:52 UTC, thedeemon wrote:
> On Monday, 18 May 2015 at 14:30:43 UTC, Chris wrote:
>
>> Why is _accessing_ an assoc treated as indexing it?
>
> Are you sure you understand "indexing" as we do? It's not like indexing of databases, it's just "accessing by index" i.e. using myarray[some_index].

I understood indexing as assigning an index to something

myarray["Index1"] = "First Entry";

As in

https://en.wiktionary.org/wiki/indexing
https://en.wiktionary.org/wiki/index#Verb