I'm new to Go programming and wondering what's the difference (if any) there between
a.
func DoSomething(a *A) {
b = a
}
b.
func DoSomething(a A) {
b = &a
}
If you are actually asking what the difference of those b's are, one is a pointer to the object passed as an argument to DoSomething, and the other is a pointer to a copy of the object passed as an argument to DoSomething.
https://play.golang.org/p/ush0hDZsdE
type A struct {
f string
}
func DoSomethingPtr(a *A) {
b := a
b.f = "hi"
}
func DoSomething(a A) {
b := &a
b.f = "hey"
}
func main() {
x := A{"hello"}
DoSomething(x)
fmt.Println(x)
DoSomethingPtr(&x)
fmt.Println(x)
}
In general, these two functions will assign different values to b. The second one makes a copy of the argument, and so the a inside the function generally has a different memory address than whatever input is passed into the function. See this playground example
package main
type A struct{
x int
}
var b *A
func d(a *A) {
b = a
}
func e(a A) {
b = &a
}
func main() {
var a = A{3}
println(&a)
d(&a)
println(b)
e(a)
println(b)
}
Interestingly, if you make the type A an empty struct instead, and initialize var a = A{}, you actually see the same value for b in the println statements.
That's because for the empty-struct type, there can only really only ever be 1 value, and its immutable, so all instances of it share the same memory address?
The variable b would be assigned a different value in each function. The values are different because one is passing a copied value and the other is passing a pointer to the original value in memory.
package main
import "fmt"
type A string
func DoSomethingPtr(a *A) {
fmt.Println(a)
}
func DoSomething(a A) {
fmt.Println(&a)
}
func main() {
x := A("hello")
DoSomething(x)
DoSomethingPtr(&x)
}
Here is the executable proof.