[ssprang]

I implement laziness "manually" all the time in Objective-C.

For example, imagine something happens which invalidates a property which must be calculated (say, a bounding box for a graphical object).

Instead of immediately recomputing it, just set it to nil, and only recompute it the next time the property is actually accessed.

This way you can harmlessly invalidate it multiple times without doing a potentially expensive calculation (which just gets thrown out by subsequent invalidations).

[theseoafs]

That's not laziness, that's just cache invalidation.

[swift]

It's fair to say that it's laziness, in my view. That sort of thing is just a manual implementation of what laziness would do in a particular situation. The closure that the thunk would hold is essentially diffused into the object that contains the lazy property.