Hi,

I know there are concerns about struct initialization in method calls but what is about struct initializer in UDA?

Scenario: I want to set several UDA values. At the moment I have to create for each value a structure with exactly 1 field. But it would be quite nice if I could use struct initialization to group these values:

struct Field
{
	string location;
	string locationName;
}

struct Foo
{
	@A = {locationName: "B"} int c; // <------------------
}

void main() {}

Of course the syntax is questionable, it is just a proposal.
What do you think?

Kind regards
André

On Thursday, 11 May 2017 at 10:49:58 UTC, Andre Pany wrote:
> Hi,
>
> I know there are concerns about struct initialization in method calls but what is about struct initializer in UDA?
>
> Scenario: I want to set several UDA values. At the moment I have to create for each value a structure with exactly 1 field. But it would be quite nice if I could use struct initialization to group these values:
>
> struct Field
> {
> 	string location;
> 	string locationName;
> }
>
> struct Foo
> {
> 	@A = {locationName: "B"} int c; // <------------------
> }
>
> void main() {}
>
> Of course the syntax is questionable, it is just a proposal.
> What do you think?
>
> Kind regards
> André

We have that syntax already.

On Thursday, 11 May 2017 at 10:51:09 UTC, Stefan Koch wrote:
> On Thursday, 11 May 2017 at 10:49:58 UTC, Andre Pany wrote:
>> Hi,
>>
>> I know there are concerns about struct initialization in method calls but what is about struct initializer in UDA?
>>
>> Scenario: I want to set several UDA values. At the moment I have to create for each value a structure with exactly 1 field. But it would be quite nice if I could use struct initialization to group these values:
>>
>> struct Field
>> {
>> 	string location;
>> 	string locationName;
>> }
>>
>> struct Foo
>> {
>> 	@A = {locationName: "B"} int c; // <------------------
>> }
>>
>> void main() {}
>>
>> Of course the syntax is questionable, it is just a proposal.
>> What do you think?
>>
>> Kind regards
>> André
>
> We have that syntax already.

I do not understand. Should the syntax I have written already work as I expect or do you mean my proposal is not possible as the syntax is ambiguous?

Kind regards
André

On Thursday, 11 May 2017 at 11:36:17 UTC, Andre Pany wrote:
> On Thursday, 11 May 2017 at 10:51:09 UTC, Stefan Koch wrote:
>> On Thursday, 11 May 2017 at 10:49:58 UTC, Andre Pany wrote:
>>> [...]
>>
>> We have that syntax already.
>
> I do not understand. Should the syntax I have written already work as I expect or do you mean my proposal is not possible as the syntax is ambiguous?
>
> Kind regards
> André
I thought it should have worked already.

My apologies the struct literal initialization syntax is unsupported because of the parser implementation.

I don't know if you would introduce new ambiguities; I suspect that you wouldn't.

On Thursday, 11 May 2017 at 11:57:01 UTC, Stefan Koch wrote:
> On Thursday, 11 May 2017 at 11:36:17 UTC, Andre Pany wrote:
>> On Thursday, 11 May 2017 at 10:51:09 UTC, Stefan Koch wrote:
>>> On Thursday, 11 May 2017 at 10:49:58 UTC, Andre Pany wrote:
>>>> [...]
>>>
>>> We have that syntax already.
>>
>> I do not understand. Should the syntax I have written already work as I expect or do you mean my proposal is not possible as the syntax is ambiguous?
>>
>> Kind regards
>> André
> I thought it should have worked already.
>
> My apologies the struct literal initialization syntax is unsupported because of the parser implementation.
>
> I don't know if you would introduce new ambiguities; I suspect that you wouldn't.

Does it make sense to open a DIP? It would make UDA quite nice to use if you can group several attributes into a struct.

Or someone know whether there are already known issues why it isn't possible?

Kind regards
André

On Thursday, 11 May 2017 at 10:49:58 UTC, Andre Pany wrote:
> Hi,
>
> I know there are concerns about struct initialization in method calls but what is about struct initializer in UDA?
>
> Scenario: I want to set several UDA values. At the moment I have to create for each value a structure with exactly 1 field. But it would be quite nice if I could use struct initialization to group these values:
>
> struct Field
> {
> 	string location;
> 	string locationName;
> }
>
> struct Foo
> {
> 	@A = {locationName: "B"} int c; // <------------------
> }
>
> void main() {}
>
> Of course the syntax is questionable, it is just a proposal.
> What do you think?
>
> Kind regards
> André

I'm not sure if it isi what you're looking for but you can do

 struct Field
 {
 	string location;
 	string locationName;
 }

 struct Foo
 {
 	@Field("","B") int c;
 }

We use this for our compiler recognised attributes in LDC, see llvmAttr for an example
(https://github.com/ldc-developers/druntime/blob/ldc/src/ldc/attributes.d#L108)

On Friday, 12 May 2017 at 10:13:02 UTC, Andre Pany wrote:
> Does it make sense to open a DIP? It would make UDA quite nice to use if you can group several attributes into a struct.
>
> Or someone know whether there are already known issues why it isn't possible?

The entire point of a DIP is to do this research for everyone and summarize it an easy-to-access and easy-to-find fashion ;-)
FWIW there is an abandoned DIP for in-place struct initialization (https://github.com/dlang/DIPs/pull/22) - it might make sense to invest the effort to revive it from the dead...

On Friday, 12 May 2017 at 10:23:34 UTC, Nicholas Wilson wrote:
> On Thursday, 11 May 2017 at 10:49:58 UTC, Andre Pany wrote:
>> Hi,
>>
>> I know there are concerns about struct initialization in method calls but what is about struct initializer in UDA?
>>
>> Scenario: I want to set several UDA values. At the moment I have to create for each value a structure with exactly 1 field. But it would be quite nice if I could use struct initialization to group these values:
>>
>> struct Field
>> {
>> 	string location;
>> 	string locationName;
>> }
>>
>> struct Foo
>> {
>> 	@A = {locationName: "B"} int c; // <------------------
>> }
>>
>> void main() {}
>>
>> Of course the syntax is questionable, it is just a proposal.
>> What do you think?
>>
>> Kind regards
>> André
>
> I'm not sure if it isi what you're looking for but you can do
>
>  struct Field
>  {
>  	string location;
>  	string locationName;
>  }
>
>  struct Foo
>  {
>  	@Field("","B") int c;
>  }
>
> We use this for our compiler recognised attributes in LDC, see llvmAttr for an example
> (https://github.com/ldc-developers/druntime/blob/ldc/src/ldc/attributes.d#L108)

I think there are cases where this syntax is more readable and there are cases where struct initialization is more readable. In the example you gave, I do not know what is the second field about and having to mention the first field feels like a burden. As developer I want the choice to decide between these 2 syntax options.

Kind regards
André

On Friday, 12 May 2017 at 10:25:07 UTC, Seb wrote:
> On Friday, 12 May 2017 at 10:13:02 UTC, Andre Pany wrote:
>> Does it make sense to open a DIP? It would make UDA quite nice to use if you can group several attributes into a struct.
>>
>> Or someone know whether there are already known issues why it isn't possible?
>
> The entire point of a DIP is to do this research for everyone and summarize it an easy-to-access and easy-to-find fashion ;-)
> FWIW there is an abandoned DIP for in-place struct initialization (https://github.com/dlang/DIPs/pull/22) - it might make sense to invest the effort to revive it from the dead...

If I find time I will create a new dip. The dip you mentioned is about a different usage scenario. My proposal is only about sructures used as UDA.
As far as I remember the old dip was not possible due to comma syntax which is now in deprecation phase.

Kund regards
André

On 05/12/2017 09:01 PM, Andre Pany wrote:
> On Friday, 12 May 2017 at 10:23:34 UTC, Nicholas Wilson wrote:
[...]
>> I'm not sure if it isi what you're looking for but you can do
>>
>>  struct Field
>>  {
>>      string location;
>>      string locationName;
>>  }
>>
>>  struct Foo
>>  {
>>      @Field("","B") int c;
>>  }
[...]
> I think there are cases where this syntax is more readable and there are
> cases where struct initialization is more readable. In the example you
> gave, I do not know what is the second field about and having to mention
> the first field feels like a burden. As developer I want the choice to
> decide between these 2 syntax options.

You can create the attribute separately:

    enum Field a = { locationName: "B" };
    @a int c;

Or if avoiding the extra symbol is more important than beauty, call a function literal:

    @((){ Field a = { locationName: "B" }; return a; }()) int c;

That's not as succinct as the syntax you propose, of course.

But your syntax (`@A = {locationName: "B"} int c;`) misses an important detail: There's no indication what the type of the attribute is (or is `A` supposed to be the type?). To make it work, you will have to add that. Something like `@Field(locationName: "B")` or `@Field{locationName: "B"}` or whatever works.

At that point, why limit it to attributes? Constructors like that would be nice everywhere. I remember such syntax being discussed repeatedly, but I don't know where we stand. Maybe there's a DIP already?