tcorpse
tcorpse
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Created by tcorpse on 7/4/2024 in #questions
UnsafePointer & Structs
would anyone be able to help me understand what is happening here? why are the outputs of the two print statements different? 
@value
struct Test:
    
    var prev: UnsafePointer[Test]
    var label: String

    fn __init__(inout self, label: String):
        self.label = label
        self.prev = UnsafePointer[Test]()

    fn __init__(inout self, label: String, prev: Test):
        self.label = label
        self.prev = UnsafePointer[Test].address_of(prev)

    fn __str__(self) -> String:
        return "Test: " + self.label

    fn next(self, label: String) -> Test:
        return Test(label, self)

fn main():

    var x = Test("x")

    print(x.next("y").prev[])
    var y = x.next("y")
    print(y.prev[])
@value
struct Test:
    
    var prev: UnsafePointer[Test]
    var label: String

    fn __init__(inout self, label: String):
        self.label = label
        self.prev = UnsafePointer[Test]()

    fn __init__(inout self, label: String, prev: Test):
        self.label = label
        self.prev = UnsafePointer[Test].address_of(prev)

    fn __str__(self) -> String:
        return "Test: " + self.label

    fn next(self, label: String) -> Test:
        return Test(label, self)

fn main():

    var x = Test("x")

    print(x.next("y").prev[])
    var y = x.next("y")
    print(y.prev[])
The output is: 
Test: x
Test:
Test: x
Test:
6 replies