How to list all the manifest constants in a class or struct

[Heromyth]

On Sunday, 17 June 2018 at 04:32:29 UTC, Jonathan M Davis wrote:
> On Sunday, June 17, 2018 02:44:38 Heromyth via 
> Digitalmars-d-learn wrote:
>> Here is a struct named S:
>>
>> struct S
>> {
>>   enum X = 10;
>>   enum Y
>>   {
>>     i = 10
>>   }
>>   enum Z = "str";
>>   struct S {}
>>   class C {}
>>
>>   static int sx = 0;
>>   __gshared int gx = 0;
>>
>>          shared void g();
>> }
>>
>> I want list all then the manifest constants in it.
>>
>> I searched the std.traits and this forums, but get nothing. 
>> Maybe, my real question is how to get the storage class for a 
>> member in a class or struct.
>
> As the storage class isn't part of the type, type introspection 
> tends to ignore it. You'll basically have to get the full list 
> of members of the type and then filter out stuff that isn't a 
> manifest constant, which is not exactly pleasant and can get a 
> bit tricky but should be possible. You'll probably have to do 
> something like filter out all of the members where you can take 
> their address and filter out all of the ones that are types, 
> and and at that point, you'd be close, but I'd have to 
> experiment to figure out whether that was enough or not or 
> whether something crept through.
>
> Andrei has been working on coming up with a better wrapper 
> around the current introspection stuff so that you'll actually 
> get data types which contain the information about a symbol 
> rather than having to figure out which combination of __traits 
> and traits from std.traits are required to get what you want. 
> So, I expect that stuff like this will get a lot easier once 
> that's ready, but in the interim, if you're trying to do 
> something less common, it can involve having to do a lot clever 
> filtering to get exactly the stuff you want and only the stuff 
> you want - and I don't think that getting the list of manifest 
> constants in a type is a very typical thing for folks to do, so 
> std.traits certainly doesn't have anything like 
> isManifestConstant.
>
> - Jonathan M Davis

Thanks for your answers. It's so glad to see some works have been 
taken for this.

The isManifestConstant is really necessary. For example, I want 
to port an Enum type from Java to D. It seems better to use a 
Struct instead of an Enum.

See here:
https://github.com/eclipse/jetty.project/blob/jetty-9.4.x/jetty-http/src/main/java/org/eclipse/jetty/http/HttpStatus.java
https://github.com/eclipse/jetty.project/blob/jetty-9.4.x/jetty-http/src/main/java/org/eclipse/jetty/http/HttpHeaderValue.java

Of course, I can define a enum for members with the basic types 
in D.
Sometimes, I like to define them in a class or struct as manifest 
constants or immutable ones. So, I need isManifestConstant.