Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Better Recursion With Swift
Search
Matt Isaacs
August 26, 2015
Programming
1
600
Better Recursion With Swift
Presented at the Brooklyn Swift Developers Meetup, August 2015.
Matt Isaacs
August 26, 2015
Tweet
Share
More Decks by Matt Isaacs
See All by Matt Isaacs
iOS Testing with Appium at Gilt
ontherocks
0
140
Mobile Testing at Gilt
ontherocks
0
47
Other Decks in Programming
See All in Programming
CloudflareのChat Agent Starter Kitで簡単!AIチャットボット構築
syumai
2
510
私の後悔をAWS DMSで解決した話
hiramax
4
210
今だからこそ入門する Server-Sent Events (SSE)
nearme_tech
PRO
3
250
個人開発で徳島大学生60%以上の心を掴んだアプリ、そして手放した話
akidon0000
1
140
Navigation 2 を 3 に移行する(予定)ためにやったこと
yokomii
0
340
「待たせ上手」なスケルトンスクリーン、 そのUXの裏側
teamlab
PRO
0
560
速いWebフレームワークを作る
yusukebe
5
1.7k
print("Hello, World")
eddie
2
530
MCPとデザインシステムに立脚したデザインと実装の融合
yukukotani
4
1.5k
@Environment(\.keyPath)那么好我不允许你们不知道! / atEnvironment keyPath is so good and you should know it!
lovee
0
120
プロパティベーステストによるUIテスト: LLMによるプロパティ定義生成でエッジケースを捉える
tetta_pdnt
0
3.3k
Design Foundational Data Engineering Observability
sucitw
3
200
Featured
See All Featured
Build your cross-platform service in a week with App Engine
jlugia
231
18k
GitHub's CSS Performance
jonrohan
1032
460k
Creating an realtime collaboration tool: Agile Flush - .NET Oxford
marcduiker
31
2.2k
The World Runs on Bad Software
bkeepers
PRO
70
11k
ReactJS: Keep Simple. Everything can be a component!
pedronauck
667
120k
Measuring & Analyzing Core Web Vitals
bluesmoon
9
580
The Web Performance Landscape in 2024 [PerfNow 2024]
tammyeverts
9
810
Gamification - CAS2011
davidbonilla
81
5.4k
Building Better People: How to give real-time feedback that sticks.
wjessup
368
19k
Six Lessons from altMBA
skipperchong
28
4k
The Art of Programming - Codeland 2020
erikaheidi
56
13k
Facilitating Awesome Meetings
lara
55
6.5k
Transcript
BETTER RECURSION WITH SWIFT
AKA…
RAIDERS OF THE LOST ARC Another reason why Swift value
types matter.
None
None
None
FAST. MODERN. SAFE
FUNCTIONAL-ISH
let str = "Favours Immutability"
GOOD: CONCURRENCY
MEH: CACHE EFFICIENCY
CHALLENGE FOR ITERATION
func factorial(n: Int) -> Int { var result = 1
var x = n while x > 0 { result = result * x x-- } return result }
RECURSION Immutable iteration!
func factorialRec(n: Int) -> Int { if n > 0
{ return n * factorialRec(n - 1) } return 1 }
ELEGANT.
YET INEFFICIENT. New call frame on each iteration.
STACK OVERFLOW Easier than ever with recursion!
All Is not Lost
TAIL CALLS Recursive call is performed last.
func tco(n: Int, acc: Int) -> Int { if n
> 0 { return tco(n - 1, acc * n) } return acc }
func tco(n: Int, acc: Int) -> Int { if n
> 0 { return tco(n - 1, acc * n) } return acc } func factorialTCO(n: Int) -> Int { return tco(n, 1) }
func tco(n: Int, acc: Int) -> Int { if n
> 0 { return tco(n - 1, acc * n) } return acc }
CAN BE OPTIMIZED To something like this…
func factorial(n: Int) -> Int { var result = 1
var x = n while x > 0 { result = result * x x-- } return result }
DOES SWIFT DO THIS?
DOES SWIFT DO THIS? The internet says: *Sometimes*
None
Or… xcrun swiftc -S
AMD64 ABI Args placed in rdi, rsi, rdx, .. Return
value -> rax
func tco(n: Int, acc: Int) -> Int rdi → n
rsi → acc rax → return value
IS TCO HAPPENING? call → Bad - Creates new stack
frame jmp, jg, jle, j… → Good - Stays in current stack frame
__TF4main3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp subq $64, %rsp cmpq
$0, %rdi movq %rdi, -8(%rbp) movq %rsi, -16(%rbp) jle LBB19_4 . . movq -24(%rbp), %rdi movq -40(%rbp), %rsi callq __TF4main3tcoFTSiSi_Si movq %rax, -56(%rbp) jmp LBB19_5 LBB19_4: movq -16(%rbp), %rax movq %rax, -56(%rbp) jmp LBB19_5 LBB19_5: movq -56(%rbp), %rax addq $64, %rsp popq %rbp retq
__TF4main3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp subq $64, %rsp cmpq
$0, %rdi movq %rdi, -8(%rbp) movq %rsi, -16(%rbp) jle LBB19_4 . . movq -24(%rbp), %rdi movq -40(%rbp), %rsi callq __TF4main3tcoFTSiSi_Si movq %rax, -56(%rbp) jmp LBB19_5 LBB19_4: movq -16(%rbp), %rax movq %rax, -56(%rbp) jmp LBB19_5 LBB19_5: movq -56(%rbp), %rax addq $64, %rsp popq %rbp retq Stack frame setup.
__TF4main3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp subq $64, %rsp cmpq
$0, %rdi movq %rdi, -8(%rbp) movq %rsi, -16(%rbp) jle LBB19_4 . . movq -24(%rbp), %rdi movq -40(%rbp), %rsi callq __TF4main3tcoFTSiSi_Si movq %rax, -56(%rbp) jmp LBB19_5 LBB19_4: movq -16(%rbp), %rax movq %rax, -56(%rbp) jmp LBB19_5 LBB19_5: movq -56(%rbp), %rax addq $64, %rsp popq %rbp retq Stack frame setup. if n > 0
__TF4main3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp subq $64, %rsp cmpq
$0, %rdi movq %rdi, -8(%rbp) movq %rsi, -16(%rbp) jle LBB19_4 . . movq -24(%rbp), %rdi movq -40(%rbp), %rsi callq __TF4main3tcoFTSiSi_Si movq %rax, -56(%rbp) jmp LBB19_5 LBB19_4: movq -16(%rbp), %rax movq %rax, -56(%rbp) jmp LBB19_5 LBB19_5: movq -56(%rbp), %rax addq $64, %rsp popq %rbp retq Stack frame setup. if n > 0
__TF4main3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp subq $64, %rsp cmpq
$0, %rdi movq %rdi, -8(%rbp) movq %rsi, -16(%rbp) jle LBB19_4 . . movq -24(%rbp), %rdi movq -40(%rbp), %rsi callq __TF4main3tcoFTSiSi_Si movq %rax, -56(%rbp) jmp LBB19_5 LBB19_4: movq -16(%rbp), %rax movq %rax, -56(%rbp) jmp LBB19_5 LBB19_5: movq -56(%rbp), %rax addq $64, %rsp popq %rbp retq Stack frame setup. if n > 0 Return value
__TF4main3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp subq $64, %rsp cmpq
$0, %rdi movq %rdi, -8(%rbp) movq %rsi, -16(%rbp) jle LBB19_4 . . movq -24(%rbp), %rdi movq -40(%rbp), %rsi callq __TF4main3tcoFTSiSi_Si movq %rax, -56(%rbp) jmp LBB19_5 LBB19_4: movq -16(%rbp), %rax movq %rax, -56(%rbp) jmp LBB19_5 LBB19_5: movq -56(%rbp), %rax addq $64, %rsp popq %rbp retq Stack frame setup. if n > 0 Return value Restore caller stack frame
__TF4main3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp subq $64, %rsp cmpq
$0, %rdi movq %rdi, -8(%rbp) movq %rsi, -16(%rbp) jle LBB19_4 . . movq -24(%rbp), %rdi movq -40(%rbp), %rsi callq __TF4main3tcoFTSiSi_Si movq %rax, -56(%rbp) jmp LBB19_5 LBB19_4: movq -16(%rbp), %rax movq %rax, -56(%rbp) jmp LBB19_5 LBB19_5: movq -56(%rbp), %rax addq $64, %rsp popq %rbp retq No TCO
OPTIMIZE
WALK: -Onone
KILL: -O
-Ounchecked
__TTSf4s_s___TF4tcoO3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp testq %rdi, %rdi jle
LBB33_4 LBB33_1: movq %rdi, %rax decq %rax jo LBB33_5 imulq %rdi, %rsi jo LBB33_5 testq %rax, %rax movq %rax, %rdi jg LBB33_1 LBB33_4: movq %rsi, %rax popq %rbp retq
__TTSf4s_s___TF4tcoO3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp testq %rdi, %rdi jle
LBB33_4 LBB33_1: movq %rdi, %rax decq %rax jo LBB33_5 imulq %rdi, %rsi jo LBB33_5 testq %rax, %rax movq %rax, %rdi jg LBB33_1 LBB33_4: movq %rsi, %rax popq %rbp retq
__TTSf4s_s___TF4tcoO3tcoFTSiSi_Si: pushq %rbp movq %rsp, %rbp testq %rdi, %rdi jle
LBB33_4 LBB33_1: movq %rdi, %rax decq %rax jo LBB33_5 imulq %rdi, %rsi jo LBB33_5 testq %rax, %rax movq %rax, %rdi jg LBB33_1 LBB33_4: movq %rsi, %rax popq %rbp retq
SOMETIMES Swift Does This.
AUTOMATIC REFERENCE COUNTING Imagine compile time garbage collection.
OLDEN TIMES Memory managed by hand.
@interface Something() { NSNumber *_numberIvar; } @end @implementation Something -
(void)setNumber:(NSNumber *)number { NSNumber *tmp = _numberIvar; _numberIvar = [number retain]; [tmp release]; } @end
@interface Something() { NSNumber *_numberIvar; } @end @implementation Something -
(void)setNumber:(NSNumber *)number { NSNumber *tmp = _numberIvar; _numberIvar = [number retain]; [tmp release]; } @end
WITH ARC
- (void)setNumber:(NSNumber *)number { _numberIvar = number; }
COMPILER MAGIC Inserts retain/release calls.
ARC in Swift Manages references.
TCO + ARC
class Integer: IntegerLiteralConvertible { let val: Int required init(integerLiteral value:
Int) { self.val = value } init(_ val: Int) { self.val = val } }
func +(lhs: Integer, rhs: Integer) -> Integer { return Integer(lhs.val
+ rhs.val) } func -(lhs: Integer, rhs: Integer) -> Integer { return Integer(lhs.val - rhs.val) } func *(lhs: Integer, rhs: Integer) -> Integer { return Integer(lhs.val * rhs.val) } func >(lhs: Integer, rhs: Integer) -> Bool { return lhs.val > rhs.val }
func factorialTC(n: Integer) -> Integer { return tc(n, 1) }
func tc(n: Integer, acc: Integer) -> Integer { if n > 0 { return tc(n - 1, acc * n) } return acc }
__TTSf4g_g___TF4tcoO2tcFTCS_7IntegerS0__S0_: pushq %rbp movq %rsp, %rbp . . leaq __TMdC4tcoO7Integer+16(%rip),
%rdi callq _swift_getInitializedObjCClass movq %rax, %rbx . . movq %rbx, %rdi callq _swift_allocObject movq %rax, %r15 . . movq %r15, %rdi movq %rbx, %rsi callq __TTSf4g_g___TF4tcoO2tcFTCS_7IntegerS0__S0_ movq %rax, %r14 movq %r15, %rdi callq _swift_release movq %rbx, %rdi callq _swift_release jmp LBB34_7 LBB34_7: movq %r14, %rax . . popq %rbp retq LBB34_8:
__TTSf4g_g___TF4tcoO2tcFTCS_7IntegerS0__S0_: pushq %rbp movq %rsp, %rbp . . leaq __TMdC4tcoO7Integer+16(%rip),
%rdi callq _swift_getInitializedObjCClass movq %rax, %rbx . . movq %rbx, %rdi callq _swift_allocObject movq %rax, %r15 . . movq %r15, %rdi movq %rbx, %rsi callq __TTSf4g_g___TF4tcoO2tcFTCS_7IntegerS0__S0_ movq %rax, %r14 movq %r15, %rdi callq _swift_release movq %rbx, %rdi callq _swift_release jmp LBB34_7 LBB34_7: movq %r14, %rax . . popq %rbp retq LBB34_8:
__TTSf4g_g___TF4tcoO2tcFTCS_7IntegerS0__S0_: pushq %rbp movq %rsp, %rbp . . leaq __TMdC4tcoO7Integer+16(%rip),
%rdi callq _swift_getInitializedObjCClass movq %rax, %rbx . . movq %rbx, %rdi callq _swift_allocObject movq %rax, %r15 . . movq %r15, %rdi movq %rbx, %rsi callq __TTSf4g_g___TF4tcoO2tcFTCS_7IntegerS0__S0_ movq %rax, %r14 movq %r15, %rdi callq _swift_release movq %rbx, %rdi callq _swift_release jmp LBB34_7 LBB34_7: movq %r14, %rax . . popq %rbp retq LBB34_8: No TCO
__TTSf4g_g___TF4tcoO2tcFTCS_7IntegerS0__S0_: pushq %rbp movq %rsp, %rbp . . leaq __TMdC4tcoO7Integer+16(%rip),
%rdi callq _swift_getInitializedObjCClass movq %rax, %rbx . . movq %rbx, %rdi callq _swift_allocObject movq %rax, %r15 . . movq %r15, %rdi movq %rbx, %rsi callq __TTSf4g_g___TF4tcoO2tcFTCS_7IntegerS0__S0_ movq %rax, %r14 movq %r15, %rdi callq _swift_release movq %rbx, %rdi callq _swift_release jmp LBB34_7 LBB34_7: movq %r14, %rax . . popq %rbp retq LBB34_8: No TCO Last Action Performed
Integer created on +,-,* ops
func +(lhs: Integer, rhs: Integer) -> Integer { return Integer(lhs.val
+ rhs.val) } func -(lhs: Integer, rhs: Integer) -> Integer { return Integer(lhs.val - rhs.val) } func *(lhs: Integer, rhs: Integer) -> Integer { return Integer(lhs.val * rhs.val) }
NEEDS RELEASING
func tc(n: Integer, acc: Integer) -> Integer { if n
> 0 { return tc(n - 1, acc * n) } return acc } SO THIS…
func tc(n: Integer, acc: Integer) -> Integer { let _n1
= n - 1 let _accn = acc * n if n > 0 { let tmp = tc(_n1, _accn) swift_release(_accn) swift_release(_n1) return tmp } return acc } IS REALLY SOMETHING LIKE
All Is sometimes Lost
FUNCTIONAL SWIFT Use value types.
VALUE SEMANTICS ≠ VALUE TYPES
SO.. BE CAREFULL
THANKS!
github.com/haveahennessy @haveahennessy
http://www.hopperapp.com/