使用Go的“测试/快速”包生成数字和字母的随机字符串

Question

I've been breaking my head over this for a few days now and can't seem to be able to figure it out. Perhaps it's glaringly obvious, but I don't seem to be able to spot it. I've read up on all the basics of unicode, UTF-8, UTF-16, normalisation, etc, but to no avail. Hopefully somebody's able to help me out here...

I'm using Go's Value function from the testing/quick package to generate random values for the fields in my data structs, in order to implement the Generator interface for the structs in question. Specifically, given a Metadata struct, I've defined the implementation as follows:

func (m *Metadata) Generate(r *rand.Rand, size int) (value reflect.Value) {
    value = reflect.ValueOf(m).Elem()
    for i := 0; i < value.NumField(); i++ {
        if t, ok := quick.Value(value.Field(i).Type(), r); ok {
            value.Field(i).Set(t)
        }
    }
    return
}

Now, in doing so, I'll end up with both the receiver and the return value being set with random generated values of the appropriate type (strings, ints, etc. in the receiver and reflect.Value in the returned reflect.Value).

Now, the implementation for the Value function states that it will return something of type []rune converted to type string. As far as I know, this should allow me to then use the functions in the runes, unicode and norm packages to define a filter which filters out everything which is not part of 'Latin', 'Letter' or 'Number'. I defined the following filter which uses a transform to filter out letters which are not in those character rangetables (as defined in the unicode package):

func runefilter(in reflect.Value) (out reflect.Value) {
    out = in // Make sure you return something
    if in.Kind() == reflect.String {
        instr := in.String()
        t := transform.Chain(norm.NFD, runes.Remove(runes.NotIn(rangetable.Merge(unicode.Letter, unicode.Latin, unicode.Number))), norm.NFC)
        outstr, _, _ := transform.String(t, instr)
        out = reflect.ValueOf(outstr)
    }
    return
}

Now, I think I've tried just about anything, but I keep ending up with a series of strings which are far from the Latin range, e.g.:

Answer 1

Confusingly the Generate interface needs a function using the type not a the pointer to the type. You want your type signature to look like

func (m Metadata) Generate(r *rand.Rand, size int) (value reflect.Value)

You can play with this here. Note: the most important thing to do in that playground is to switch the type of the generate function from m Metadata to m *Metadata and see that Hi Mom! never prints.

In addition, I think you would be better served using your own type and writing a generate method for that type using a list of all of the characters you want to use. For example:

type LatinString string
const latin = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz01233456789"

and then use the generator

func (l LatinString) Generate(rand *rand.Rand, size int) reflect.Value {
    var buffer bytes.Buffer
    for i := 0; i < size; i++ {
        buffer.WriteString(string(latin[rand.Intn(len(latin))]))
    }
    s := LatinString(buffer.String())
    return reflect.ValueOf(s)
}

playground

Edit: also this library is pretty cool, thanks for showing it to me