String

Use v.String(value, name?, title?) and v.StringP(&value, ...).

Common rules:

v.Is(v.String("Dennis").EqualTo("Dennis"))
v.Is(v.String("").Empty())
v.Is(v.String(" ").Blank())
v.Is(v.String("processing").InSlice([]string{"idle", "processing"}))

Length: bytes vs characters

Byte-based:

v.Is(v.String("123456").MaxBytes(6))
v.Is(v.String("123").MinBytes(3))
v.Is(v.String("1234").OfByteLength(4))

Rune-based (characters):

v.Is(v.String("虎視眈々").MaxLength(4))
v.Is(v.String("虎視眈々").OfLengthBetween(2, 4))

Regex

regex, _ := regexp.Compile("pre-.+")
v.Is(v.String("pre-approved").MatchingTo(regex))

Pointer-specific rules

var s *string
v.Is(v.StringP(s).Nil())