Query individual runes under cursor position.

[hexaflex-zz]

The View type has a Word and Line method. I am finding myself in need of looking at individual runes under the current cursor position.

This is useful when implementing extended editor functionality like moving the cursor left or right by a whole words, or deleting a whole word at a time. These require one to scan backward or forward from the current cursor position, until a whitespace character is encountered. A View.Rune(x, y int) (rune, error) function allows us to do this in a nice and clean fashion.

I implemented it myself, but it requires access to the unexperted realPosition function.

// Rune returns the rune at the given position.
func (v *View) Rune(x, y int) (rune, error) {
    x, y, err := v.realPosition(x, y)
    if err != nil {
        return 0, err
    }

    if x < 0 || y < 0 || y >= len(v.lines) || x >= len(v.lines[y]) {
        return 0, errors.New("invalid point")
    }

    return v.lines[y][x].chr, nil
}