So, User-Defined Attributes

[Philippe Sigaud]

On Fri, Jan 4, 2013 at 9:59 PM, Andrei Alexandrescu <
SeeWebsiteForEmail at erdani.org> wrote:

> On 1/4/13 3:51 PM, Walter Bright wrote:
>
>>

> So, I'm testing how to transfer UDA from one symbol to another.
>>>
>>
>>
>> This will do the transfer:
>>
>> import std.stdio;
>> void main()
>> {
>> @(3, "hello") int i = 10;
>> @(__traits(getAttributes, i)) double d2;
>> writeln("[",__traits(**getAttributes, d2), "]");
>> }
>>
>
Yes, I know. I just want to automate the process. I want a function or some
piece of code that can propagate attributes.
For example, say I receive a piece of unvalidated input. I test it and it's
OK. I want to return it, with a new attribute (say, Validated() ),while
keeping the input attributes. Since it seems a common need, I was looking
for a way to abstract the process somewhat.

For now, we would return a Validated(initialValue) struct. I just want to
see how attributes can be used here. It seems that:

@(Validated, __traits(getAttributes, input)) InputType temp;
return temp;

do not work.

If attribute manipulation cannot be isolated in easily reusable code, that
would be sad.



Andrei:

>
> For transfer templates are better than attributes.


Could you please give an example?
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