go

What is the meaning of '*' and '&'?


I am doing the http://tour.golang.org/. Could anyone explain this function to me, specifically lines 1, 3, 5, and 7? I am particularly curious about what the '*' and '&' symbols do. What are they supposed to do when mentioned in a function declaration? A toy example:

    1: func intial1(var1 int, var2 int, func1.newfunc[]) *callproperfunction {
    2:
    3:    addition:= make ([] add1, var1)
    4:    for i:=1;i<var2;i++ {
    5:       var2 [i] = *addtother (randomstring(lengthofcurrent))
    6:    }
    7:    return &callproperfunction {var1 int, var2 int, func1.newfunc[], jackpot}
    8: }

It seems that they are pointers, similar to what we have in C++. However, I am having trouble connecting these concepts to what we have here. In other words, what do '*' and '&' do when used in a function declaration in Go?

I understand what reference and dereference mean. What I cannot understand is how we can use a pointer to a function in Go. For example, in lines 1 and 7, what do these two lines do? Is the function named initial1 declared to return a pointer? And in line 7, are we calling it with arguments using the returned function?


Solution

  • This is possibly one of the most confusing things in Go. There are basically 3 cases you need to understand:

    The & Operator

    & goes in front of a variable when you want to get that variable's memory address.

    The * Operator

    * goes in front of a variable that holds a memory address and resolves it (it is therefore the counterpart to the & operator). It goes and gets the thing that the pointer was pointing at, e.g. *myString.

    myString := "Hi"
    fmt.Println(*&myString)  // prints "Hi"
    

    or more usefully, something like

    myStructPointer = &myStruct
    // ...
    (*myStructPointer).someAttribute = "New Value"
    

    * in front of a Type

    When * is put in front of a type, e.g. *string, it becomes part of the type declaration, so you can say "this variable holds a pointer to a string". For example:

    var str_pointer *string
    

    So the confusing thing is that the * really gets used for 2 separate (albeit related) things. The star can be an operator or part of a type.