Clang's technical specification of ARC goes into much more detail about how the qualifiers work.
But, to answer your question: assign
and __unsafe_unretained
are not the same thing. assign
is a property attribute that tells the compiler how to synthesise the property's setter implementation, while __unsafe_unretained
is an ownership qualifier that tells ARC how to insert retain
/release
calls. But they are related: when declaring a property, assign
implies __unsafe_unretained
ownership.
Prior to ARC, assign
was the default property ownership qualifier; but with ARC enabled, the default for retainable object pointer types is strong
. (For scalars and other pointer types, assign
is still the default.)
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