add memory post

Author: sonjh1217

_posts/2025-09-23-iOS-memory.md

@@ -0,0 +1,69 @@
+---
+title:  "iOS Memory"
+
+categories:
+  - iOS
+  - Memory
+tags:
+  - Memory
+---
+
+## App Memory's Four Segments
+
+![image](./assets/img/post/Memory.drawio.png)
+
+1. **Code**: Machine code compiled from source code
+1. **Data**: Global variables, static variables, static literals
+1. **Heap**: Dynamically allocated data (size and lifetime determined at runtime)
+    1. Reference types
+        1. Class objects
+    1. Internal buffers of arrays, strings, and dictionaries 
+        1. But they behave like value types via copy-on-write
+    1. Escaping closures' captured contexts & mutable capture boxes
+        1. May include value types when needed
+        1. Because the closure must be able to access them later when it executes
+    1. Lifetime Managed by ARC
+1. **Stack segment**: Function call frames
+    1. Return addresses, saved registers, storage slots for parameters and local variables, temporaries
+    1. Lifetime managed automatically in LIFO order when the scope ends
+    1. One per thread
+    1. Limited capacity, so deep recursion can cause a stack overflow
+
+## Closure's captured contexts & mutable capture boxes
+1. A closure’s code resides in the code (text) segment.<br> A closure value consists of a code pointer and a context pointer.<br> That value is stored wherever the variable or property that holds the closure is stored.
+1. Escaping Closure: the closure can be stored and executed later
+1. Captured Contexts & mutable capture boxes
+
+![image](./assets/img/post/closureCapture.drawio-2.png)
+
+~~~
+let f = { print("hi") } // no capture -> no context
+
+let x = 10
+let g = { print(x) } // context: [x=10], no boxes 
+
+var n = 0
+let c2 = { print(n) } // context: [&box], box(n)
+
+var n = 0
+let c3 = { n += 1 } // context: [&box], box(n)
+~~~
+{: .language-swift}
+
+## Reference Types & Value Types
+
+1. Reference Types
+    1. `Class`
+    1. `Actor`
+    1. Closure
+    1. `NSObject`
+    1. UIKit/AppKit types (e.g., `UIView`, `UIColor`)
+1. Value Types
+    1. Primitive types: `Int`, `Float`, `Double`, `Bool`, `Character`
+    1. `String`
+    1. Collection types: `Array`, `Set`, `Dictionary`
+    1. `Tuple`
+    1. `Struct`
+    1. `Enum`
+        1. `Optional`
+