How do I initialize a pointer to pointer in golang?

Question

How do I initialize a struct with a double pointer field? I am trying to initialize a struct as below:

type atype struct {
  val string
}

a := &struct {
    StringValue string
    Pointer **atype
}{
    StringValue: "FOO",
//this is the relevant bit
    Pointer : &(&atype{ 
      val: "test"
    })
}

This gives me an error : invalid pointer type **basicAppConfig for composite literal

What is wrong in my logic? I take the pointer to a pointer to the value.

I also tried to use

reflect.PtrTo(&atype{
    val: "string"
})

without success...

If you're ok with initializing only to first pointer, having the pointed-to pointer be nil, you can use new to your heart's content. play.golang.org/p/995hzR3EVWQ — mkopriva
– mkopriva, Commented Feb 15, 2018 at 23:31

Kaedys · Accepted Answer · 2018-02-15 22:08:11Z

8

Pointers are not addressable unless assigned to a variable. The ability to take the address of a composite literal without assigning it to a variable is limited to structs, arrays, slices, and maps.

To do what you want to do, you have to assign the pointer to a variable first, after which you can assign the address of that (pointer) variable within the struct literal:

https://play.golang.org/p/7WyS732H3cZ

package main

type atype struct {
    val string
}

func main() {
    at := &atype{
        val: "test",
    }

    a := &struct {
        StringValue string
        Pointer     **atype
    }{
        StringValue: "FOO",
        Pointer:     &at,
    }

    _ = a
}

References:

answered Feb 15, 2018 at 22:08

Kaedys

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