如何在界面上使用Sscan

Question

I'm using to fmt.Sscan convert a string to any type, here is what I'm doing:

package main

import (
    "fmt"
    "reflect"
)

func test() interface{} {
    return 0
}

func main() {
    a := test() // this could be any type
    v := "10" // this could be anything

    fmt.Println(reflect.TypeOf(a), reflect.TypeOf(&a))

    _, err := fmt.Sscan(v, &a)
    fmt.Println(err)
}

This code is failing because Sscan doesn't accept interfaces as the second value: can't scan type: *interface {}. demo

What I find most weird is that the first print prints: int *interface {}, is it a int or an interface?

How can I assert a to the right type (it could be any primitive)? Is there a solution that doesn't include a giant switch statement?

Thank you.

Answer 1

Here's how to convert a string to a value of any type supported by the fmt package:

// convert converts s to the type of argument t and returns a value of that type.
func convert(s string, t interface{}) (interface{}, error) {

    // Create pointer to value of the target type
    v := reflect.New(reflect.TypeOf(t))

    // Scan to the value by passing the pointer SScan 
    _, err := fmt.Sscan(s, v.Interface())

    // Dereference the pointer and return the value.
    return v.Elem().Interface(), err
}

Call it like this:

a := test()
a, err := convert("10", a)
fmt.Println(a, err)

Run it on the Playground