Reference counting in practice.
WHAT THE MODEL IS
Memory released when nothing references it, tracked automatically.
WHAT THAT AVOIDS
A garbage collector, and its pauses.
WHAT IT REQUIRES ATTENTION TO
Reference cycles.
WHAT A CYCLE IS
Two objects holding strong references to each other, so neither is ever released.
WHERE THEY COMMONLY OCCUR
Closures capturing the object that owns them Delegate relationships Parent and child references
WHAT SOLVES IT
Declaring one reference as not owning.
WHAT THE TWO NON-OWNING KINDS ARE
One becoming empty when the object is released One assuming the object outlives it, crashing if not
WHAT TO PREFER
The safer of the two, unless you are certain.
WHAT TO DO IN CLOSURES
Capture the owning object weakly, and check it still exists.
WHAT A LEAK LOOKS LIKE
Memory rising as screens are opened and closed, never falling.
WHAT TO USE TO FIND THEM
The instrumentation tools, showing retained objects and cycles.
WHAT TO TEST
Opening and closing a screen repeatedly, watching memory.
