[swift-evolution] Re-initialization of lazy variables?

[Spencer Kohan]

Hi all,

In migrating to swift 4 I've noticed one thing which has changed is there
is no longer support for the automatic re-initialization of lazy
variables.

In swift 3 I could declare a variable like this:

    lazy var myVar : MyType! = {
        return makeMyVar()
    }()

And then if I wanted that initialization block to be executed again, I
could just nullify the variable:

    self.myVar = nil

It looks as if this was never intentional, and according to this bug report
<https://bugs.swift.org/browse/SR-5172>, and now the nullified variable
stay null rather than executing the initialization block a second time.

Has the possibility been discussed of providing a way to force lazy vars to
initialize more than once?  Working with swift 3 I found this behavior to
be very useful in some use cases.  For example in computer graphics it's a
nice way to handle the generation of assets which only need to be created
in the case of some relatively infrequent event, like for instance a window
resize.  It seems I'm not alone - the top stack-overflow question
<https://stackoverflow.com/questions/25072597/re-initialize-a-lazy-initialized-variable-in-swift>
related to re-initializing lazy variables has over 10k views, so I suppose
others have found a use case for this functionality as well.

Cheers,
Spencer Kohan
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