Collections

This is the chapter you cannot skim. Slices and maps are in almost every Go program you will ever read, and they come with enough sharp edges that a surface-level understanding guarantees bugs down the line.

Arrays come first because slices are built on them. Seven lessons on slices walk through the basics, length and capacity, append, slicing, the aliasing trap, copy, and deleting or comparing, then a tour of the slices package for the modern generic helpers. Maps get three lessons (comma-ok idiom, deletion, deliberately random iteration), followed by the maps package for generic map helpers. A short strings tour and a word-counter mini-project finish the chapter.

Move through the lessons in order. The slice lessons in particular build on each other: by the end you will understand why append sometimes "loses" elements if you are not careful, and why copy exists.