Slot Chunking

Slot extraction turns a template string into a flat list of chunks.

1. Chunk

anza::engine::slot::Chunk (defined in src/engine/slot/parse.rs):

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Chunk {
  Static(Vec<u8>),
  Slot(String),
  Raw(String),
}

• Chunk::Static: HTML bytes, written to the output as is.
• Chunk::Slot: the trimmed placeholder name ({{ user_name }} becomes "user_name"). HTML-escaped when the engine runs with escape: true.
• Chunk::Raw: the name of a raw placeholder ({{{ content }}}), always inserted as is.

2. extract

anza::engine::slot::extract(template: &str) -> anza::Result<Vec<Chunk>> scans the string once:

1. Find the next {{; the text before it becomes a Chunk::Static.
2. If it is {{{, find the next }}} and push a Chunk::Raw; otherwise find the next }} and push a Chunk::Slot with the trimmed text between.
3. The rest of the string becomes a final Chunk::Static.

An unclosed {{ or {{{, or an empty placeholder, returns Error::Template. There is no other syntax: no loops, conditionals, filters or comments.

use anza::engine::slot::{extract, Chunk};

let chunks = extract("<div class=\"user\">{{name}} is {{status}}</div>")?;

assert_eq!(chunks.len(), 5);
assert_eq!(chunks[1], Chunk::Slot("name".into()));
assert_eq!(chunks[3], Chunk::Slot("status".into()));
// chunks[0], [2] and [4] are Chunk::Static

3. Binding

Each Template compiles its chunks once into an anza::engine::slot::Plan (in src/engine/slot/bind.rs): static text plus slot positions, with each distinct name looked up once per bind. Template::bind runs the plan. For each placeholder, the value comes from params.resolve(name); a missing value writes nothing.

To bind chunks without a Template, use the free functions (they compile a Plan on every call, so keep a Template or Plan for repeated binds):

pub fn string<P: Params + ?Sized>(chunks: &[Chunk], params: &P) -> Result<String>;
pub fn string_with<P: Params + ?Sized>(chunks: &[Chunk], params: &P, escape: bool) -> Result<String>;
pub fn inject<P: Params + ?Sized, W: std::io::Write>(chunks: &[Chunk], params: &P, out: &mut W) -> Result<()>;
pub fn inject_with<P: Params + ?Sized, W: std::io::Write>(chunks: &[Chunk], params: &P, escape: bool, out: &mut W) -> Result<()>;

4. Escaping

With escape off (the default, and in string / inject), {{name}} and {{{name}}} both write values as is, without HTML escaping. With escape on (Setup::escape, or string_with / inject_with with true), {{name}} values are passed through anza::escape_html and {{{name}}} values stay raw. escape_html maps & < > " ' to & < > " ', which is safe in element content and quoted attribute values.