How Does Go's Pass-by-Value Mechanism Mimic Pass-by-Reference Using Pointers?

Understanding Passing by Reference and Value in Go Functions

In Go, the concept of passing by reference and value can be confusing at first. To clarify, it's worth noting that Go primarily supports passing by value. However, when passing a pointer to an object, it mimics passing by reference.

To understand this, consider the following Java function:

databaseFunction(DatabaseType db) {
  // do something
}

In this code, the DatabaseType instance db is passed to the function by value. However, in Go, it might be represented as:

func PutTasks(db *sql.DB) echo.HandlerFunc {

}

In the Go example, the asterisk * before sql.DB implies that the function expects a pointer to a sql.DB instance. This is because in Go, values of pointer types hold addresses.

According to the cheat sheet you mentioned, the syntax func PrintPerson(p *Person) indicates that the function only accepts a pointer address to a Person object. The reason for using a pointer here is to enable the function to modify the original object that was passed in.

To further demonstrate, consider the following Go code:

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!
}

In this example, x is a pointer to an integer. By dereferencing it, we can directly modify the value it points to. However, re-assigning x to point to a different variable has no impact on the caller since they only have a copy of the pointer variable, not the value it originally pointed to.

Therefore, using pointers provides a mechanism for sharing values between the caller and the function, allowing changes made within the function to be reflected back to the original object.

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