Stdlib Essentials

Advanced · Standard Library & I/O

A tour of packages you’ll reach for constantly.

• stdlib1 — encoding/json: struct tags + (un)marshaling
• stdlib2 — io.Reader/io.Writer + io.Copy
• stdlib3 — slices (Go 1.21+) generic helpers
• stdlib4 — time: the reference-layout parse/format scheme

Resources

• Go by Example: JSON
• Go blog: The io.Reader interface
• pkg.go.dev: slices · time
• Go by Example: Time Formatting / Parsing

Exercises

stdlib1 test

stdlib1 — encoding/json

Show hint

Struct tags map JSON keys to fields:

Name string `json:"full_name"`
Age  int    `json:"user_age"`

Source

stdlib2 test

stdlib2 — io.Reader / io.Writer

Show hint

io.Copy streams a Reader into a Writer:

if _, err := io.Copy(&buf, r); err != nil { return "", err }

Source

stdlib3 test

stdlib3 — slices

Show hint

Sort ascending then reverse:

slices.Sort(out)
slices.Reverse(out)

Source

stdlib4 test

stdlib4 — time

Show hint

The layout string IS the reference date Mon Jan 2 2006:

return time.Parse("2006-01-02", s)

Source

stdlib5 test

stdlib5 — strconv

Show hint

strconv.Atoi parses a base-10 int:

n, err := strconv.Atoi(s); if err != nil { return 0, err }; return n*2, nil

Source

stdlib6 test

stdlib6 — regexp

Show hint

Compile once, then match:

re := regexp.MustCompile(`^[^@\s]+@[^@\s]+\.[^@\s]+$`)
return re.MatchString(s)

Source