Error: struct Type is not an expression

Question

Using struct and a function that is supposed to print out the struct's elements, I have written this simple program:

package main

import "fmt"

type Salutation struct {
    name     string
    greeting string
}

func Greet(salutation Salutation) {
    fmt.Println(salutation.name)
    fmt.Println(salutation.greeting)
}

func main() {
    var s = Salutation
    s.name = "Alex"
    s.greeting = "Hi"
    Greet(s)
}

When I run it I get the error go:16: type Salutation is not an expression. What goes wrong here?

Interestingly enough, when I change the definition of s to var s = Salutation {"Alex", "Hi"} it works just fine. But they are basically different syntactic ways to define the same entity. That's why I don't understand the source of the error.

Answer 1

The error is on this line

    var s = Salutation

The thing to the right of the = must evaluate to a value. Salutation is a type, not value. Here are three ways to declare s:

 var s Salutation      // variable declaration using a type 

 var s = Salutation{}  // variable declaration using a value

 s := Salutation{}     // short variable declaration

The result of all three declarations is identical. The third variation is usually preferred to the second, but cannot be used to declare a package-level variable.

See the language specification for all of the details on variable declarations.

The variable declaration and field initializations can be combined into a single statement:

 var s = Salutation{name: "Alex", greeting: "Hello"} // variable declaration

 s := Salutation{name: "Alex", greeting: "Hello"}    // short variable declaration

Answer 2

4th way:

var s *Salutation = &( Salutation{} );

I always pass structs by reference, not value. And always pass primitives by value.

Your method re-written as a reciever method:

func (s *Salutation) Greet()() {
    fmt.Println(s.name)
    fmt.Println(s.greeting)
}

Full Example:

package main

import "fmt"

func NewSalutation()(*Salutation){
    return &( Salutation{} );
}
type Salutation struct {
    name     string
    greeting string
}

func (s *Salutation) Greet()() {
    fmt.Println(s.name)
    fmt.Println(s.greeting)
}

func main() {
    var s *Salutation;   //:<--Null
    s = NewSalutation()  //:<--Points To Instance
    s.name     = "Alex"
    s.greeting = "Hi"
    s.Greet();
}