Lesson 02 · A key equals value line

A key equals value line

The heart of TOML is the line key = value. Today you read one such line, split it at the equals sign, and store the pair in the table, using a plain decimal integer as the first value type so the whole pipeline works end to end.

The goal

Parse a single key = value line with a decimal integer into a one-entry table.

Start here - the target

TO DO

Scenario: One key/value pair

Giventhe input answer = 42

WhenParse is called

Thenthe table has one entry whose key is answer and whose value is the integer 42

Andsurrounding spaces do not matter: x=1 and x = 1 both give key x with the integer 1

Background

A TOML key/value pair is written key = value, one per line. Parsing it is two moves: split the line at the first =, then make sense of each side. The left side is the key and the right side is the value. Whitespace around the = and around each side is insignificant, so trim it before you look at either part.

For the value you need something concrete to store, so start with the simplest type TOML offers: a decimal integer. Read the trimmed right-hand text as a base-10 number and wrap it in a Value of KindInteger. This gives the library its first real round trip - text in, a typed value out - and establishes the parseValue step that every later value form plugs into. The key today is a plain bare key; its full character rules and quoted forms come in the next lessons.

Make it work

// for each non-blank line:
//   split once on the first '=' into keyText and valueText
//   key   := trimSpace(keyText)      // a bare key for now
//   value := parseValue(trimSpace(valueText))
//   append Entry{key, value} to the table
// parseValue today: strconv.ParseInt(text, 10, 64) -> KindInteger

CheckpointDONE

A single key = value line becomes one table entry. Commit and stop here.