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January 06, 2013
Accessing UDA of private field
I'm trying to adapt my serialization library, Orange, to use the new 
UDA's. Currently I have one template, NonSerialized, that I want to 
transfer to an UDA. This template works like:

class Foo
{
    int a;
    int b;

    mixin NonSerialized!(b);
}

When serializing Foo "b" will not be serialized. What the template does 
is adding a static field to the class, like this:

class Foo
{
    int a;
    int b;

    static enum __nonSerialized = ["b"];
}

Which I then can extract and use to exclude the fields from serialization.

This works fine to transfer to an UDA except in one case. That is when 
the field is not public. Orange will serialize all fields, regardless of 
the protection they have. I accomplish this by using the "tupleof" 
property of the class.

The problem is that to access a UDA attached to a field I need to pass a 
symbol to the __traits(getAttributes). With "tupleof" I can get the 
name, type and value of a field but I cannot get a symbol.

__traits(getMember) can be used to get the symbol but that will only 
work for public fields.

Does anyone have another solution? I had really hoped I could use UDA's 
in Orange.

https://github.com/jacob-carlborg/orange

-- 
/Jacob Carlborg
January 06, 2013
Re: Accessing UDA of private field
Hello Jacob

I believe this would be possible using topleof once this
http://d.puremagic.com/issues/show_bug.cgi?id=9178 issue is taken care of.
Kindly vote it up. :-)


Regards
- Puneet
January 06, 2013
Re: Accessing UDA of private field
> The problem is that to access a UDA attached to a field I need to pass a
> symbol to the __traits(getAttributes). With "tupleof" I can get the name,
> type and value of a field but I cannot get a symbol.
>
> __traits(getMember) can be used to get the symbol but that will only work
> for public fields.
>

You can use a string mixin:

class Foo
{
   int a;
   @(3) private int b;
}

void main()
{
   writeln(mixin("__traits(getAttributes, " ~ Foo.tupleof[1].stringof ~
")")); // -> 3
}
January 06, 2013
Re: Accessing UDA of private field
> You can use a string mixin:
>
> class Foo
> {
>     int a;
>     @(3) private int b;
> }
>
> void main()
> {
>     writeln(mixin("__traits(getAttributes, " ~ Foo.tupleof[1].stringof ~
> ")")); // -> 3
> }
>
>
>

Hmm....

This works only when main is in the same file (and therefor module) as Foo.

Regards
- Puneet
January 06, 2013
Re: Accessing UDA of private field
On Sun, Jan 6, 2013 at 7:46 PM, d coder <dlang.coder@gmail.com> wrote:

>
> You can use a string mixin:
>>
>> class Foo
>> {
>>     int a;
>>     @(3) private int b;
>> }
>>
>> void main()
>> {
>>     writeln(mixin("__traits(getAttributes, " ~ Foo.tupleof[1].stringof ~
>> ")")); // -> 3
>> }
>>
>>
>>
>
> Hmm....
>
> This works only when main is in the same file (and therefor module) as Foo.
>
>
Yes, but the OP question was to get the attributes in a generic way. The
interesting part is the mixin, the rest is just scaffolding to print a
result.
If Jacob adopts this solution, he can insert these mixins where he needs
them.
January 06, 2013
Re: Accessing UDA of private field
On 2013-01-06 18:29, Philippe Sigaud wrote:

> You can use a string mixin:
>
> class Foo
> {
>      int a;
>      @(3) private int b;
> }
>
> void main()
> {
>      writeln(mixin("__traits(getAttributes, " ~ Foo.tupleof[1].stringof
> ~ ")")); // -> 3
> }

Good thinking. It's not pretty but it works. Thanks.

-- 
/Jacob Carlborg
January 06, 2013
Re: Accessing UDA of private field
> Good thinking. It's not pretty but it works. Thanks.


Maybe it can be hidden inside a template?
January 07, 2013
Re: Accessing UDA of private field
On 2013-01-06 23:33, Philippe Sigaud wrote:
>
>     Good thinking. It's not pretty but it works. Thanks.
>
>
> Maybe it can be hidden inside a template?

Yeah, I'll see what I can do.

-- 
/Jacob Carlborg
January 07, 2013
Re: Accessing UDA of private field
On Monday, 7 January 2013 at 10:19:45 UTC, Jacob Carlborg wrote:
> On 2013-01-06 23:33, Philippe Sigaud wrote:
>>
>>    Good thinking. It's not pretty but it works. Thanks.
>>
>>
>> Maybe it can be hidden inside a template?
>
> Yeah, I'll see what I can do.

in which context does private fail? I'm using something like this:

struct my_struct
{
private:
  @(1) int t1;
  @(2) int t2;
  @(3) int t3;
}

foreach(m; __traits(allMembers, my_struct))
  with(my_struct.init)
    pragma(msg, __traits(getAttributes, mixin(m)));
January 07, 2013
Re: Accessing UDA of private field
On 2013-01-07 12:59, Tove wrote:

> in which context does private fail? I'm using something like this:
>
> struct my_struct
> {
> private:
>    @(1) int t1;
>    @(2) int t2;
>    @(3) int t3;
> }
>
> foreach(m; __traits(allMembers, my_struct))
>    with(my_struct.init)
>      pragma(msg, __traits(getAttributes, mixin(m)));

Using a mixin works.

-- 
/Jacob Carlborg
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