Re: Writing XML

[Jacob Carlborg]

On 2011-02-06 15:43, Tomek Sowiński wrote:
While I'm circling the problem of parsing, I took a quick look at writing not 
to get stuck in analysis-paralysis. Writing XML is pretty independent from 
parsing and an order of magnitude easier to solve. It was perfect to get myself 
coding.
These are the guidelines I followed:

  * Memory minimalism: don't force allocating an intermediate node structure 
just to push a few tags down the wire.

  * Composability: operating on an arbitrary string output range.

  * Robustness: tags should not be left open, even if the routine producing tag 
interior throws.

  * Simplicity of syntax: resembling real XML if possible.

  * Space efficiency / readability: can write tightly (without indents and 
newlines) for faster network transfer and, having easy an means for temporary 
tight writing, for better readability.

  * Ease of use:
    - automatic to!string of non-string values,
    - automatic string escaping according to XML standard,
    - handle nulls: close the tags short (<tag/>), don't write attributes with 
null values at all.

  * anything else?


The new writer meets pretty much all of the above. Here's an example to get a 
feel of it:

auto books = [
     Book([Name("Grębosz", "Jerzy")], "Pasja C++", 1999),
     Book([Name("Navin", "Robert", "N.")], "Mathemetics of Derivatives", 2007),
     Book([Name("Tokarczuk", "Olga")], "Podróż ludzi Księgi", 1996),
     Book([Name("Graham", "Ronald", "L."),
          Name("Knuth", "Donald", "E."),
          Name("Patashnik", "Oren")], "Matematyka Konkretna", 2008)
];

auto outputRange = ... ;
auto xml = xmlWriter(outputRange);

xml.comment(books.length, " favorite books of mine.");
foreach (book; books) {
     xml.book("year", book.year, {
          foreach (author; book.authors) {
              xml.tight.authorName({
                  xml.first(author.first);
                  xml.middle(author.middle);
                  xml.last(author.last);
              });
          }
          xml.tight.title(book.title);
     });
}

--------------------------------- program output 
---------------------------------

<!-- 4 favorite books of mine. -->
<book year="1999">
   <authorName><first>Jerzy</first><middle/><last>Grębosz</last></authorName>
   <title>Pasja C++</title>
</book>
<book year="2007">
   
<authorName><first>Robert</first><middle>N.</middle><last>Navin</last></authorName>
   <title>Mathemetics of Derivatives</title>
</book>
<book year="1996">
   <authorName><first>Olga</first><middle/><last>Tokarczuk</last></authorName>
   <title>Podróż ludzi Księgi</title>
</book>
<book year="2008">
   
<authorName><first>Ronald</first><middle>L.</middle><last>Graham</last></authorName>
   
<authorName><first>Donald</first><middle>E.</middle><last>Knuth</last></authorName>
   <authorName><first>Oren</first><middle/><last>Patashnik</last></authorName>
   <title>Matematyka Konkretna</title>
</book>


Questions and comments?

This seems to be like the Ruby "builder" library, which is a library I 
like. This is a perfect candidate for the syntax sugar I've proposed for 
passing delegates to a function after the parameter list.

--
/Jacob Carlborg