Assign count variable over calling .count on Array in Swift

Let's investigate! Is myArray.count equivalent to accessing a stored property or is it a computed property performing some \"unnecessary\" calculations if called repeatedly for a non-mutated array? (Disregarding compiler cleverness)\n\n\nswift/stdlib/public/core/Arrays.swift.gyb\n\n\n\n/// The number of elements in the array.\npublic var count: Int {\n return _getCount()\n}\n\n// ... what is function _getCount()?\n\ninternal func _getCount() -> Int {\n return _buffer.count\n}\n\n// ... what is property _buffer?\ninternal var _buffer: _Buffer\n\n// ... what is type _Buffer? (Swift)\ninternal typealias _Buffer = _ContiguousArrayBuffer<Element>\n\n// ... what is type _ContiguousArrayBuffer?\n// --> switch source file\n\n\n\n\nswift/stdlib/public/core/ContiguousArrayBuffer.swift\n\n\n\nimport SwiftShims\n\n/// Class used whose sole instance is used as storage for empty\n/// arrays. The instance is defined in the runtime and statically\n/// initialized. See stdlib/runtime/GlobalObjects.cpp for details.\ninternal struct _ContiguousArrayBuffer<Element> : _ArrayBufferProtocol {\n\n // ... conformance to _ArrayBufferProtocol\n\n /// The number of elements the buffer stores.\n internal var count: Int {\n get {\n return __bufferPointer.header.count\n }\n // ...\n } \n // ...\n}\n\n// ... what is property __bufferPointer?\nvar __bufferPointer: ManagedBufferPointer<_ArrayBody, Element>\n\n// what is type _ArrayBody?\n// we notice for now that it is used in the following class:\ninternal final class _EmptyArrayStorage\n : _ContiguousArrayStorageBase {\n // ...\n\n var countAndCapacity: _ArrayBody // telling name for a tuple? :)\n}\n\n// --> proceed to core/ArrayBody.swift\n\n\n\n\nswift/stdlib/public/core/ArrayBody.swift\n\n\n\nimport SwiftShims\n\n// ...\n\ninternal struct _ArrayBody {\n var _storage: _SwiftArrayBodyStorage\n\n // ...\n\n /// The number of elements stored in this Array.\n var count: Int {\n get {\n return _assumeNonNegative(_storage.count)\n }\n set(newCount) {\n _storage.count = newCount\n }\n } \n}\n\n// we are near our price! we need to look closer at _SwiftArrayBodyStorage, \n// the type of _storage, so lets look at SwiftShims, GlobalObjects.cpp\n// (as mentioned in source comments above), specifically\n// --> switch source file\n\n\n\n\nswift/stdlib/public/SwiftShims/GlobalObjects.h\n\n\n\nstruct _SwiftArrayBodyStorage {\n __swift_intptr_t count; \n __swift_uintptr_t _capacityAndFlags;\n};\n\n// Yay, we found a stored property!\n\n\n\nSo in the end count is a stored property and is not computed per call, so it should be no reason to explicitly store the arr.count property by yourself.",

struct _SwiftArrayBodyStorage {\n __swift_intptr_t count;\n __swift_uintptr_t _capacityAndFlags;\n};\n\n\nthis is the struct that Swift implements. According to this count is there all the time knowing how many elements are in buffer. You probably can use that \n\ninfo form: https://ankit.im/swift/2016/01/08/exploring-swift-array-implementation/\n\nedit for more info \n\npublic var count: Int {\n get {\n return __bufferPointer.value.count\n }\n nonmutating set {\n _sanityCheck(newValue >= 0)\n\n _sanityCheck(\n newValue <= capacity,\n \"Can't grow an array buffer past its capacity\")\n\n __bufferPointer._valuePointer.memory.count = newValue\n }\n}\n",

It doesn't matter; I'd suggest just doing whatever makes your code simpler and easier to understand. In release builds, the optimizer should inline and notice that the value will be the same across calls. Regardless, Array.count is basically equivalent in performance/codegen to accessing a local variable.",