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I want to understand what is stored in the stack and heap in swift. I have a rough estimation: Everything that you print and the memory address appears not the values, those are stored in the stack, and what is printed out as values, those are on the heap, basically according to value and reference types. Am I completely wrong? And optionally, could you provide a visual representation of the stack/heap?
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Stack is a linear data structure whereas Heap is a hierarchical data structure. Stack memory will never become fragmented whereas Heap memory can become fragmented as blocks of memory are first allocated and then freed. Stack accesses local variables only while Heap allows you to access variables globally.
The Heap Space contains all objects are created, but Stack contains any reference to those objects. Objects stored in the Heap can be accessed throughout the application. Primitive local variables are only accessed the Stack Memory blocks that contain their methods.
Variables allocated on the stack are stored directly into memory and access memory very faster and its allocation dealt with compile time. Variable allocated on the heap have their memory allocated at run time and accessing their memory is bit slower.
If the programmer uses large structures or size arrays, they would be better off using the heap as you can allocate a large size to it. If the programmer just needs tiny variables that only need the quick ins and outs, then utilizing the stack would be the better choice.
As @Juul stated Reference types are stored in the Heap and values in the stack.
Here is the explanation:
Stack and Heap
Stack is used for static memory allocation and Heap for dynamic memory allocation, both stored in the computer's RAM .
Variables allocated on the stack are stored directly to the memory, and access to this memory is very fast, and its allocation is determined when the program is compiled. When a function or a method calls another function which in turns calls another function, etc., the execution of all those functions remains suspended until the very last function returns its value. The stack is always reserved in a LIFO order, the most recently reserved block is always the next block to be freed. This makes it really simple to keep track of the stack. Freeing a block from the stack is nothing more than adjusting one pointer.
Variables allocated on the heap have their memory allocated at run time, and accessing this memory is a bit slower, but the heap size is only limited by the size of virtual memory. Elements of the heap have no dependencies with each other and can always be accessed randomly at any time. You can allocate a block at any time and free it at any time. This makes it more complex to keep track of which parts of the heap are allocated or free at any given time.
For Escaping Closure:
An important note to keep in mind is that in cases where a value stored on a stack is captured in a closure, that value will be copied to the heap so that it's still available by the time the closure is executed.
For more reference: http://net-informations.com/faq/net/stack-heap.htm
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Classes (reference types) are allocated in the heap, value types (like Struct, String, Int, Bool, etc) live in the stack. See this topic for more detailed answers: Why Choose Struct Over Class?
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