Struct vs Class
[Stack vs Heap]
[Value vs Reference type]
Struct is more preferable. But Struct does not solve all issues by default. Usually you can hear that value type is allocated on stack, but it is not always true. Only local variables are allocated on stack
//simple blocks
struct ValueType {}
class ReferenceType {}
struct StructWithRef {
let ref1 = ReferenceType()
}
class ClassWithRef {
let ref1 = ReferenceType()
}
func foo() {
//simple blocks
let valueType1 = ValueType()
let refType1 = ReferenceType()
//RetainCount
//StructWithRef
let structWithRef1 = StructWithRef()
let structWithRef1Copy = structWithRef1
print("original:", CFGetRetainCount(structWithRef1 as CFTypeRef)) //1
print("ref1:", CFGetRetainCount(structWithRef1.ref1)) //2 (originally 3)
//ClassWithRef
let classWithRef1 = ClassWithRef()
let classWithRef1Copy = classWithRef1
print("original:", CFGetRetainCount(classWithRef1)) //2 (originally 3)
print("ref1:", CFGetRetainCount(classWithRef1.ref1)) //1 (originally 2)
}
*You should not use/rely on retainCount, because it does not say useful information
To check stack or heap
During compiling SIL(Swift Intermediate Language)Swift Intermediate Language(SIL) can optimize you code
swiftc -emit-silgen -<optimization> <file_name>.swift
//e.g.
swiftc -emit-silgen -Onone file.swift
//emit-silgen -> emit-sil(is used in any case)
//-emit-silgen Emit raw SIL file(s)
//-emit-sil Emit canonical SIL file(s)
//optimization: O, Osize, Onone. It is the same as Swift Compiler - Code Generation -> Optimization Level
There you can find alloc_stack(allocation on stack) and alloc_box(allocation on heap)