Lesson 21 · Nested table headers

Nested table headers

Grouping goes deeper than one level. Today you parse a dotted table header, which names a nested table and creates the intermediate tables along the way.

The goal

Parse a [a.b.c] header, creating intermediate tables a and b.

Start here - the target

TO DO

Scenario: A dotted table header

Giventhe document with a line reading open-bracket a.b.c close-bracket, then x = 1

WhenParse is called

Thenthe root has a table a, containing a table b, containing a table c, containing x with the integer 1

Andeach dotted segment names one level, and a quoted segment such as "b.c" is a single key with a dot in its name, not two levels

Background

Real config nests more than one level deep - [servers.alpha.network] - and TOML writes that as a dotted table header. Each dot separates a level, so [a.b.c] names the table c inside b inside a. If any of those intermediate tables does not exist yet, the header creates it on the way down, so a single header can bring a whole branch into being.

Implement it by splitting the header name into segments and walking from the root, descending into each named child and creating it when it is missing, until you reach the last segment; that deepest table becomes the new current table. One subtlety in the split: a quoted segment is one key even if it contains a dot, so ["b.c"] (with the quotes) is a single table named b.c, whereas [b.c] (bare) is c inside b. Respecting quotes while splitting keeps names with dots intact, the same way quoted keys did back in the first chapter.

Make it work

// split the header name on '.' into segments (respecting quotes)
// walk from the root, and for each segment:
//   if a child table with that name exists, descend into it
//   otherwise create it, then descend
// set current = the deepest table

CheckpointDONE

Dotted headers build nested tables, creating intermediates. Commit and stop here.