Cast a struct pointer to interface pointer in Golang

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There is no such thing as a “pointer to an interface” (technically, you can use one, but generally you don’t need it).

As seen in “what is the meaning of interface{} in golang?“, interface is a container with two words of data:

  • one word is used to point to a method table for the value’s underlying type,
  • and the other word is used to point to the actual data being held by that value.

interface

So remove the pointer, and doStuff will work just fine: the interface data will be &ms, your pointer:

func doStuff(inout interface{}) {
   ...
}

See this example:

ms := MyStruct{1}
doStuff(&ms)
fmt.Printf("Hello, playground: %v\n", ms)

Output:

Hello, playground: {1}

As newacct mentions in the comments:

Passing the pointer to the interface directly works because if MyStruct conforms to a protocol, then *MyStruct also conforms to the protocol (since a type’s method set is included in its pointer type’s method set).

In this case, the interface is the empty interface, so it accepts all types anyway, but still.

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