Why Does Using a Value Receiver Lead to Incorrect Slice Modification in a Go Struct?

Removing Elements from a Slice in a Struct (Resolved)

In the code snippet provided, there is an issue when attempting to remove an element from a slice within a struct using a value receiver. This leads to the incorrect modification of the slice in the original struct.

To resolve this, a pointer receiver must be used in the method that modifies the slice. This is because Go value receivers create a copy of the receiver value, which means any changes made to the receiver in the method are not reflected in the original struct.

Here is the corrected code:

func (guest *Guest) removeFriend(id int) {
    for i, other := range guest.friends {
        if other == id {
            guest.friends = append(guest.friends[:i], guest.friends[i+1:]...)
            break
        }
    }
}

By using a pointer receiver (*Guest), the method modifies the original Guest struct's friends slice, ensuring that the element is removed correctly.

Explanation:

When a slice is passed by value, the receiver method operates on a copy of the slice. When modifications are made to the slice, they are only reflected in the copy, not in the original slice. However, using a pointer receiver allows the method to modify the original slice, as the receiver is now a pointer to the original struct.

Example Usage:

guest := &Guest{
    id:      1,
    name:    "Bob",
    surname: "Pats",
    friends: []int{1, 2, 3, 4, 5},
}

fmt.Println(guest)
guest.removeFriend(3)
fmt.Println(guest)

Output:

&{1 Bob Pats [1 2 3 4 5]}
&{1 Bob Pats [1 2 4 5]}

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