Finding UDAs with Templates

[Jacob Carlborg]

On 2013-07-23 06:27, Paul O'Neil wrote:
> I'm trying to write some code that finds all the members of a class that
> have a particular user defined attribute.  My current attempt is at
> https://github.com/todayman/d_template_experiments/tree/8fccd27d7d5557ec6e2f0614374cf5f79fe80b4c
>
>
> I would like to have a static method that returns an array of strings of
> the names of the members with the "@Sync" attribute.  I use the
> allMembers trait to get the list of strings, then try to filter out the
> ones I want.  There are problems when I convert from the string to a
> symbol / something to get the attributes.  Right now, I'm getting errors
> like:

I tried your code and this should be enough:

import std.typetuple;

static bool doesFieldSync (string field) ()
{
     alias attrs = TypeTuple!(__traits(getAttributes, mixin("FileData." 
~ field)));
     return staticIndexOf!(Sync, attrs) != -1;
}

The important things here are that __traits(getAttributes) returns a 
tuple. You cannot assign a tuple to a variable. But you can alias it. 
When you alias it you do need to use this wrapper TypeTuple, I don't 
remember why but that's how it works.

// This is the method I'm trying to write
static string[] syncableFields() {
     auto result = new string[0];
     foreach( key ; __traits(derivedMembers, FileData) )
     {
         if( doesFieldSync!key() ) {
             result ~= key;
         }
     }
     return result;
}

Here I used derivedMembers instead of allMembers, this is want you want, 
most times.

But I see that there are some problems with some members. These members 
are mixed in "mixin Signal". So if you try to filter out these members. 
I would just hard code them.

-- 
/Jacob Carlborg