Reference counting in practice.
WHAT THE MODEL IS
References counted automatically, with memory released when the count reaches zero.
WHAT IT 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 released.
WHERE THEY OCCUR
Closures capturing the object that owns them Delegate relationships Parent and child references
WHAT THE TWO NON-OWNING KINDS ARE
One becoming nothing when the object is released One assuming the object outlives it, crashing otherwise
WHAT TO PREFER
The safer one, unless you are certain.
WHAT TO DO IN CLOSURES
Capture the owning object weakly, and check it still exists.
WHAT VALUE TYPES AVOID
All of this, since they are not reference counted.
WHY THAT IS A REASON TO PREFER THEM
Fewer opportunities for cycles.
WHAT A LEAK LOOKS LIKE
Memory rising as screens are opened and closed, never falling.
WHAT TO USE TO FIND IT
The memory graph, showing what retains an object.
WHAT TO TEST
Opening and closing a screen repeatedly.
