automatic ref counting - Type and declaration restrictions on Swift capture specifiers -

automatic ref counting - Type and declaration restrictions on Swift capture specifiers -

i'm confused type requirements , declaration restrictions swift capture specifiers. documentation says weak references must var , "of optional type", , unowned references must of non-optional type. apple's own api reference has examples of unowned(unsafe) references declared optionals, while xcode interface builder creates weak outlets , actions implicitly unwrapped (which not "of optional type" in language reference).

what types required each of swift capture specifiers? must var , can let?

fwiw, think its

weak can type? or type!, not type; , must var unowned(safe) (same unowned) must type; , may let unowned(unsafe) can type? or type!; , may let

but i'm far sure.

first cocoaor cocoa touch apis imported in swift fromobjective-c`. mapped in swift best possible ways.so both can interoperable.

those unowned(unsafe) properties marked assign in objc. these unsafe , arc doesn't retain object, , doesn't create sure reference gets reset nil if object deallocated. these old apple api , not changed arc , remain asassignbut should makedelegateweak` not headers best practices in swift have made many tricks create swift , objective-c interoperable , if headers loose safety swift proveide.

you right

weak should optional contain nil automatically if objects deallocate , no other pointer retain

unowned(safe) should not optional , not reset nilif objects deal-located

unowned(unsafe) can or can not optional not provide safety arc object deal-location , not reset nil.you should not utilize in swift program.use unowned if needed.it interoperability.

weak var because can changed when objects deallocate , set nil.

unowned(safe) , unowned(unsafe) can both var or let dependent on , run-time not alter these variables.

note:you can not declare unowned(unsafe) optional in swift program.its interoperability , should not used in swift.they have made because of assign or unretain properties can nil

swift automatic-ref-counting optional