What is the difference between a stack and a heap?

Stack and Heap are two memory areas used for storing data in programs.

Stack:

• Used for storing local variables and return addresses of functions.
• Operates on the LIFO (Last In, First Out) principle.
• Automatic memory management: memory is allocated when entering a function and freed upon exit.
• Faster than heap due to simplicity of management and data locality.
• Fixed or limited size, stack overflow can occur.

Heap:

• Used for dynamic memory allocation of objects that can persist after the current function exits.
• Memory management is manual (via malloc/free in C/C++) or automatic (ARC/Garbage Collection/Ownership in Swift/Rust).
• Slower than stack due to more complex management and possible fragmentation.
• Size is more flexible and limited only by available system memory.
• Memory leaks can occur if allocated memory is not freed.

Comparison:

Feature	Stack	Heap
Operation principle	LIFO	No specific order
Memory management	Automatic	Manual or automatic (ARC/GC/Ownership)
Speed	Faster	Slower
Usage	Local variables, return addresses	Dynamically allocated objects, reference types
Size	Fixed / Limited	Flexible
Possible issues	Stack overflow	Memory leak, fragmentation

In Swift, Value Types (e.g., struct, enum, primitive types like Int, Bool) are usually stored on the stack, while Reference Types (e.g., class, closure) are stored on the heap. Variables, even of reference types, can be stored on the stack due to compiler optimizations (escape analysis).