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Created by tac on 9/12/2023 in #questions
__moveinit__ and __del__
When the __del__ method is not implemented, the __moveinit__ method is less likely to be invoked. Why is this the case? Consider the following example code: 
struct Pair:
    var x: Int
    var y: Int

    fn __init__(inout self, x: Int, y: Int):
        print("Running init")
        self.x = x
        self.y = y
    
    fn __moveinit__(inout self, owned existing: Self):
        print("move init")
        self.x = existing.x
        self.y = existing.x

    fn __copyinit__(inout self, existing: Self):
        print("copy init")
        self.x = existing.x
        self.y = existing.y

fn copy(owned pair: Pair) -> Pair:
    return pair

fn main():
    let p = Pair(1, 2)
    let moved = copy(p^)
    let moved2 = moved^
struct Pair:
    var x: Int
    var y: Int

    fn __init__(inout self, x: Int, y: Int):
        print("Running init")
        self.x = x
        self.y = y
    
    fn __moveinit__(inout self, owned existing: Self):
        print("move init")
        self.x = existing.x
        self.y = existing.x

    fn __copyinit__(inout self, existing: Self):
        print("copy init")
        self.x = existing.x
        self.y = existing.y

fn copy(owned pair: Pair) -> Pair:
    return pair

fn main():
    let p = Pair(1, 2)
    let moved = copy(p^)
    let moved2 = moved^
On execution, the output is: 
copy init
move init
copy init
move init
However, when we include the __del__ method as follows: 
struct Pair:
    # omitted
    fn __del__(owned self):
        print("deleted")

fn copy(owned pair: Pair) -> Pair:
    return pair

fn main():
    let p = Pair(1, 2)
    let moved = copy(p^)
    let moved2 = moved^
struct Pair:
    # omitted
    fn __del__(owned self):
        print("deleted")

fn copy(owned pair: Pair) -> Pair:
    return pair

fn main():
    let p = Pair(1, 2)
    let moved = copy(p^)
    let moved2 = moved^
The output changes to: 
move init
move init
deleted
move init
move init
deleted
The presence or absence of the __del__ method impacts the sequence of method calls __copyinit__ and __moveinit__, potentially affecting the performance. Why does this occur?
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