XML Archive Tag Names

[hoensr]

Hello!

So, suppose I have this DTO:

struct Foo
{
    std::vector<int> BarList;

    template<class Archive>
    void serialize(Archive & archive)
    {
        archive(
            CEREAL_NVP(BarList)
            );
    }
};

Cereal will serialize it to XML like this:

<?xml version="1.0" encoding="utf-8"?>
<cereal>
        <BarList size="dynamic">
                <value0>18</value0>
                <value1>20</value1>
                <value2>2</value2>
                <value3>3</value3>
                <value4>4</value4>
        </BarList>
</cereal>

There are three things I don't like about this XML:

1. The "cereal" root tag... This is solved by PR 321.
2. I'd like to have a different inner tag name than the funny "value0", "value1", ...
3. I don't need the size="dynamic" attribute. What was it good for, anyway?

Therefore, I have forked the repo and added some patches for these issues. Of course, the default behaviour is unchanged, but since I didn't want to add another boolean argument (don't you just love these Options(true, true, false, true, false) constructors??), I went for sort of a fluent interface.

Now with this code:

struct Foo
{
    std::vector<int> BarList;

    template<class Archive>
    void serialize(Archive & archive)
    {
        archive(
            CEREAL_NVP(BarList).withInnerName("Bar")
            );
    }
};

    {
        Foo foo{ { 18, 20, 2, 3, 4 } };
        cereal::XMLOutputArchive xmlwrite(
            std::cout, 
            cereal::XMLOutputArchive::Options(4, true, false, "MyFoo").NoSizeAttributes());
        foo.serialize(xmlwrite);
    }

My XML looks like this:

<?xml version="1.0" encoding="utf-8"?>
<MyFoo>
        <BarList>
                <Bar>18</Bar>
                <Bar>20</Bar>
                <Bar>2</Bar>
                <Bar>3</Bar>
                <Bar>4</Bar>
        </BarList>
</MyFoo>

So, my additions were:

1. I have added the withInnerName function to the NameValuePair to control the name of the inner XML tags.
2. I have added the NoSizeAttribute function to the XMLOutputArchive::Options class to get rid of the attribute.

My branch is currently here. Since I have not so much experience with creating pull requests and having them merged, I'd first like to ask whether this addition is interesting?

Then, since I gather there are already people thinking about a different Options structure, maybe it would be nice to have more understandable options, something like this?

Options().Precision(4).NoIndent().NoSizeAttributes()

[AzothAmmo]

Regarding your enumerated points first:

1. I will hopefully get around to merging this soon since 1.3 is our next big milestone.
2. The default naming scheme is just one that supports out of order loading. I don't see anything wrong with allowing it to be changed.
3. This actually serves no direct functional purpose internally. It exists to let a human know that cereal could potentially handle them directly manipulating the number of elements here and their program would not crash when loading. Consider an std::array instead of an std::vector, although in both cases cereal can get the number of elements from parsing the XML, for the array, bad things will happen if too many elements are read or written into the fixed sized array.

I'm definitely a fan of cleaning up the options interface. It was fine when we had only a few options but it is starting to become very unwieldy, as you demonstrated.

I'm not sure I like the interface you propose for the "inner name" of NVP values, though I do like giving this as an option. It might just be the naming I don't like, I'd need to think about it more.

If you do decide to make a PR, try to distill each major change into its own independent PR. All of these changes would also need to be mirrored in the JSON archive as well (which you don't have to do), but know that it would be part of merging any of them.

[hoensr]

Hi Azoth,

thank you for your kind reply! I have created two pull requests for my two changes:

• Added withInnerName to set the names of the inner XML tags for lists #400
• Add option to turn off the size=dynamic attributes of lists #401

Hope this is helpful.
Of course, feel free to change the details (naming, options handling etc.) to your liking.

About JSON, I don't really see a need to touch it, because in JSON the result is already fine as it is:

{
    "BarList": [
        18,
        20,
        2,
        3,
        4
    ]
}

[AzothAmmo]

#401 merged

[AzothAmmo]

Closing as #400 is self contained.