确定var是否为自定义类型

Question

How to determine if the var passed to my Func is actually the Type that i want?

i have a custom Type

type Name string

and a bunch of constants of that type

const Fred Name = "fred"

and i have a func that i need to forbid any other type of input other than my custom Type ex:

func MyFunc(name1 Name, name2 Name) (*Person, error) {
//bunch of stuff
}

how i check inside my func that name1 and name2 are not strings passed to the func but exclusively the const i already defined in my type ex:

p, err := MyFunc(Fred,Albert) //What i want
p, err := MyFunc("fred","albert") //What i dont want to happen

if cannot answer my question how i can make like a Enum in Golang a type that means something and restrict other ppl to use that type i defined

Answer 1

Short version? you can't create that restricting kind of enum.

Long version, there are few options:

Define a validation function on the "type":

func (n Name) valid() bool { //private method
    switch n {
    case Mal, Kaylee: //all the valid constants
        return true
    }
    return false
}

This however doesn't stop someone from using Name("fred").valid() like @peterSO pointed out.

Use a struct with a private member in it, however they aren't "constants" per-se, an outside package can reassign them to invalid values:

type Name struct {
    n string
}

var (
    invalid = Name{}
    Mal     = Name{"mal"}
    Kaylee  = Name{"kaylee"}
)

func MyFunc(name1 Name, name2 Name) error {
    if name1 == invalid || name2 == invalid {
        return errors.New("invalid names")
    }
    return nil
}

Use numeric constants and a private array, this is the only fool-proof version really and the closest you will get to a real enum:

type Name uint8

var names = [...]string{
    "Mal",
    "Kaylee",
}

func (n Name) valid() bool {
    return uint8(n) < uint8(len(names))
}

func (n Name) String() string {
    if !n.valid() {
        return "invalid"
    }
    return names[n]
} 

const (
    Mal Name = iota
    Kaylee
)

func MyFunc(name1 Name, name2 Name) error {
    if !name1.valid() || !name2.valid() {
        return errors.New("invalid names")
    }
    return nil
}