I've seen a lot of examples of how to get a list of User Defined Attributes from a known symbol but I haven't seen any for how to get a list of symbols when only the UDA is known.

The use case is the same as seen in Rust with Serde[1]. Library users annotate a struct to mark it for serialization. In Java and Spring, you can mark a method with @Secured to add authorization to an endpoint[2]. In both of these cases, you have no idea which symbol the UDA will be applied to.

So far I've only seen a way to get unknown UDAs from known symbols but not how to get unknown symbols from UDAs. Is there any documentation for how to get a list of symbols annotated with a specific UDA?


1: Serde: https://github.com/serde-rs/json
2: Spring: https://www.baeldung.com/spring-security-method-security

On Tuesday, 12 May 2020 at 02:51:39 UTC, Doug wrote:
> So far I've only seen a way to get unknown UDAs from known symbols but not how to get unknown symbols from UDAs. Is there any documentation for how to get a list of symbols annotated with a specific UDA?

see std.traits.getSymbolsByUDA

http://dpldocs.info/experimental-docs/std.traits.getSymbolsByUDA.html

there's some caveats, like it only searches one particular parent symbol for its children

(that's because the way this works is you reflect through children checking each symbol child's uda list to see if it is present)

but it basically works for many things at least contained per-module. you can pass each module you care about in though to generate a more full list

On Tuesday, 12 May 2020 at 02:53:53 UTC, Adam D. Ruppe wrote:
>
> see std.traits.getSymbolsByUDA

Thanks for the link. I did see that one. But that function searches within known symbols. My use case if for a library that's used outside of my application. In that case, I wouldn't know which symbol a library applies an annotation to. This is why I asked for how to get a list of unknown symbols from a known UDA.

To use a REST frame work as an example, I would supply a @GET annotation and a user would apply that annotation to a handler method. I wouldn't know the method or module in advanced so I wouldn't know which symbol to pass to "getSymbolsByUDA" of any of it's sibling functions.

I'm curious to see what I'd be able to do if this is possible.

On 5/11/20 11:30 PM, Doug wrote:
> On Tuesday, 12 May 2020 at 02:53:53 UTC, Adam D. Ruppe wrote:
>>
>> see std.traits.getSymbolsByUDA
> 
> Thanks for the link. I did see that one. But that function searches within known symbols. My use case if for a library that's used outside of my application. In that case, I wouldn't know which symbol a library applies an annotation to. This is why I asked for how to get a list of unknown symbols from a known UDA.
> 
> To use a REST frame work as an example, I would supply a @GET annotation and a user would apply that annotation to a handler method. I wouldn't know the method or module in advanced so I wouldn't know which symbol to pass to "getSymbolsByUDA" of any of it's sibling functions.
> 
> I'm curious to see what I'd be able to do if this is possible.

So the idea is that you know the parent symbol.

In the case of serialization/deserialization, you give an instance of a type to serialize or deserialize. Then the library can search the symbols inside that type to see if any has the UDA you are looking for.

In the Rust example, there is a line of code:

let p: Person = serde_json::from_str(data)?;

I'm assuming that this conversion is detected and figured out (i.e. this is how serde "finds" the type desired). For D, it would look something like:

auto p = serde_json.from_str!Person(data);

If you want a list of ALL symbols that have the UDA in the application, that would require some form of runtime reflection (like Java). D has very limited support for runtime reflection. In D, you would use some form of registration to tell the system about your symbols.

-Steve

On Tuesday, 12 May 2020 at 04:02:18 UTC, Steven Schveighoffer wrote:

> In the case of serialization/deserialization, you give an instance of a type to serialize or deserialize. Then the library can search the symbols inside that type to see if any has the UDA you are looking for.
>
> In the Rust example, there is a line of code:
>
> let p: Person = serde_json::from_str(data)?;
>
> I'm assuming that this conversion is detected and figured out (i.e. this is how serde "finds" the type desired). For D, it would look something like:
>
> auto p = serde_json.from_str!Person(data);
>
> If you want a list of ALL symbols that have the UDA in the application, that would require some form of runtime reflection (like Java). D has very limited support for runtime reflection. In D, you would use some form of registration to tell the system about your symbols.
>
> -Steve

Thanks for the feedback.
I've got a better idea of what is and isn't possible now.

I'll see about looking at one or two D JSON libraries to see how they approach things. It should help shed some more light on the subject.

On 2020-05-12 06:02, Steven Schveighoffer wrote:

> If you want a list of ALL symbols that have the UDA in the application, that would require some form of runtime reflection (like Java). D has very limited support for runtime reflection. In D, you would use some form of registration to tell the system about your symbols.

I think it's possible to implement the `RTInfo` template in `object.d`. But that requires a custom druntime.

`RTInfo` is a template that is instantiated once for each type in the program.

-- 
/Jacob Carlborg