lazy variable with closure

Question

In this article, it says (referencing the code below): "You must use lazy to prevent the closure for being created more than once."

private lazy var variable:SomeClass = {
    let fVariable = SomeClass()
    fVariable.value = 10
    return fVariable
}()

Why would lazy prevent the closure from being created more than once? And why would the lack of lazy cause it to evaluate more than once?

Answer 1

The tutorial code you quote is this:

private lazy var variable:SomeClass = {
    let fVariable = SomeClass()
    fVariable.value = 10
    return fVariable
}()

Contrast it with this:

private var variable:SomeClass {
    let fVariable = SomeClass()
    fVariable.value = 10
    return fVariable
}

The first one initializes variable to a newly created SomeClass instance, once at most (and maybe not even that many times). The second one is a read-only computed variable and creates a new SomeClass instance every time its value is read.