7.7.2. PUGIXML-02 — Building XML

This tutorial covers constructing XML documents from scratch using pugixml/PUGIXML_boost — the tag/attr EDSL, builder helpers, and serialization to strings.

7.7.2.1. Creating an empty document

with_doc allocates a new xml_document, invokes a block, and frees it automatically:

with_doc() <| $(doc) {
    var dnode = doc as xml_node
    var root = append_child(dnode, "greeting")
    set(root.text, "Hello!")
    print(to_string(doc))
}

7.7.2.2. The `tag` builder EDSL

tag() creates child elements using pipe + block syntax for nesting. Three overloads:

tag(name, block) — element with nested content
tag(name, text) — leaf element with text
tag(name) — bare element

with_doc() <| $(doc) {
    doc |> tag("library") <| $(var library) {
        library |> tag("book") <| $(var book) {
            book |> tag("title", "The C Programming Language")
            book |> tag("author", "Kernighan")
            book |> tag("year", "1988")
        }
    }
    print(to_string(doc))
}

Output:

<?xml version="1.0"?>
<library>
  <book>
    <title>The C Programming Language</title>
    <author>Kernighan</author>
    <year>1988</year>
  </book>
</library>

7.7.2.3. Attribute chaining

attr() appends an attribute and returns the parent node, enabling fluent chaining:

var display = config |> tag("display")
display |> attr("width", 1920) |> attr("height", 1080) |> attr("fullscreen", true)

attr has overloads for string, int, float, and bool.

7.7.2.4. Builder helpers

Lower-level helpers for when you don’t need the pipe+block pattern:

Function	Description
`add_child(node, name, text)`	Append element with text content
`add_child_ex(node, name, attr, val)`	Append element with one attribute
`add_attr(node, name, value)`	Append typed attribute (string/int/float/bool)

add_child(root, "name", "Alice")
add_child_ex(root, "skill", "name", "daslang")
add_attr(root, "score", 95)

7.7.2.5. Serializing to string

to_string works on both documents and individual nodes:

to_string(doc) — full document with <?xml version="1.0"?>
to_string(node) — subtree only, no declaration
node as string — same as to_string(node)

7.7.2.6. Dynamic building with loops

tag and attr work naturally inside loops:

with_doc() <| $(doc) {
    doc |> tag("leaderboard") <| $(var board) {
        for (i in range(3)) {
            board |> tag("player") <| $(var p) {
                p |> attr("rank", i + 1)
                p |> tag("name", names[i])
                p |> tag("score", "{scores[i]}")
            }
        }
    }
}