Passing by reference and value in Go to function

In PHP development, the Go to function is a very commonly used function that can be used to control the flow of the program. When using the Go to function, we have two ways of passing parameters: by reference and by value. When parameters are passed by reference, modifications to the parameters inside the function will affect the variable values ​​outside the function. When parameters are passed by value, modifications to the parameters inside the function will not affect the variable values ​​outside the function. Therefore, when writing functions, we need to choose the appropriate parameter transfer method according to actual needs to achieve the expected program logic. In this article, I will introduce in detail the usage and difference of passing by reference and value in the Go to function to help readers better understand and apply this important PHP function.

Question content

I'm a little confused about passing by reference and value in go.

I've seen explanations for the * in front of the type.

* in front of a type name, means that the declared variable will store an address of another variable of that type (not a value of that
type).

This makes no sense to me.

In java if I pass a database instance to a function I would do this

databasefunction(databasetype db) {
      // do something
}

But in the go example, I've passed it like this.

func puttasks(db *sql.db) echo.handlerfunc {

}

Why do we need to add an asterisk in front of the type?

Based on this cheat sheet, I found out.

func PrintPerson(p *Person)   ONLY receives the pointer address
(reference)

I don't understand why I only want to send the pointer address as parameter.

Solution

First of all, go technically only passes by value. When you pass a pointer to an object, you pass the pointer by value, not the object by reference. The differences are subtle, but sometimes relevant. For example, you can overwrite a pointer value that has no effect on the caller, rather than dereferencing it and overwriting the memory it points to.

// *int means you *must* pass a *int (pointer to int), NOT just an int!
func someFunc(x *int) {
    *x = 2 // Whatever variable caller passed in will now be 2
    y := 7
    x = &y // has no impact on the caller because we overwrote the pointer value!
}

Regarding your question "Why do we need an asterisk in front of the type?": The asterisk means that the value is a pointer to the sql.db type, not sql.db type of value. These are not interchangeable!

Why send the pointer address? This way you can share values ​​between the caller of the function and the function body, and have changes made inside the function reflected in the caller (e.g. a pointer is the only way a "setter" method can act to the object). This is actually what your java code is doing as well; in java you always access objects by reference (pointer), so java does this automatically rather than letting you explicitly instruct it . But in go you can also access objects via pointers, so you have to be explicit. If you call a function and pass in an object directly, the function will get a copy of the object, and if the function modifies the object, the caller will not see those changes. Therefore, if you want changes to propagate outside the function, you must pass a pointer. This way, the pointer will be copied, but the object it points to will be shared. See also:

Tour section about pointers

, Go specification section about pointers , Go to address operator specification section

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