Lesson 25 · Moving the cursor - Build a Fuzzy Finder

Moving the cursor

A finder lets you move a highlight up and down the result list. Today you add that movement, clamped so it never runs off either end.

The goal

Move the selection down and up through the results, clamped to the first and last positions.

Start here - the target

TO DO

Scenario: Clamped selection movement

Givena Finder with three results and the selection at index 0

Whendown is pressed three times, then up is pressed three times

Thenthe selection goes 0, 1, 2, 2 (it stops at the last result, index 2, and does not wrap), then 2, 1, 0, 0 (it stops at the first result and does not go negative)

Background

The finder’s cursor is a single index into the results, and moving it is just incrementing or decrementing that index. The only real decision is what happens at the ends. Clamping - stopping at the first and last result - is the behavior most finders use and the easiest to reason about: pressing down at the bottom leaves you at the bottom, pressing up at the top leaves you at the top.

The edges are the whole lesson, so pin them: down at the last result must not wrap to the top, and up at the first must not go negative and crash the next render. An empty result list is the degenerate case - with zero results the selection simply stays at 0 and both moves are no-ops. Getting this boundary logic right now means the keystroke handling later can dispatch an arrow key straight to these methods without re-checking anything.

Make it work

func (f *Finder) Down() {
  if f.Selection < len(f.Results)-1 { f.Selection++ }
}
func (f *Finder) Up() {
  if f.Selection > 0 { f.Selection-- }
}

CheckpointDONE

The selection moves through the results and stops cleanly at both ends. Commit and stop here.