DIP6: Attributes

[Daniel Keep]

Ary Borenszweig wrote:
> Daniel Keep wrote:
>>
>> grauzone wrote:
>>> ...
>>> For example serialization. How do you specify that a field shouldn't be
>>> part of the serialized data? Java has an extra keyword attribute like
>>> "transient" (comes from before attributes were introduced). C# uses what
>>> we call annotation in this thread. How would you do this in D?
>>
>> struct Foo
>> {
>>     int serialise_me, dont_serialise_me, or_me;
>>
>>     alias Tuple!("dont_serialise_me", "or_me") IgnoreForSerialisation;
>> }
>>
>> Or, if you'd rather have a less hacky interface:
>>
>> struct Foo
>> {
>>     int serialise_me, dont_serialise_me, or_me;
>>
>>     mixin IgnoreForSerialisation!("dont_serialise_me", "or_me");
>> }
> 
> ...
> 
> That looks great. And as your struct grows, you have to scroll down to
> see how an element is serialized. And if you want to change how an
> element is serialized you scroll down and move two strings from one
> point to another. I also wonder *how* is that mixed template
> implemented, it probably adds some fields or things to that struct.

"How would you do this in D?"

I was answering the question.

> How about this:
> 
> struct Foo {
> 
>     @XmlElement("desiredNameForOne");
>     char[] one;
> 
>     @XmlElement("desiredNameForTwo");
>     int two;
> 
>     @XmlAttribute("desiredNameForThree");
>     float three;
> }
> 
> Which one looks nicer and more understandable to you? How do you change
> a property to be serialized as an element to an attribute? You just
> change "XmlElement" to "XmlAttribute" and that's it.

Which one works right now and doesn't require you first spend at least a
year convincing Walter that it's useful, then convincing him it's
necessary, followed by six months of continuous bike-shedding by the
community before Walter gives up and implements something that somehow
manages to piss off everyone who was arguing for it, largely because it
wasn't the exact syntax they wanted?

Which one have I been successfully using in a project of mine for over
two and a half years now thanks to it also working in crusty old D1?

Who's the one with a working struct->xml parser template based on it?

> Your approach also is no DRY: you have to name the fields again. It
> might throw awful compiler errors for template code when you mistype
> something. If you rename a field you must also remember to rename the
> serialization mixin.

It's odd; I can't find the part of my post where I said this was perfect
and the ideal solution!  My newsreader must be truncating my messages...