Eugene Yagrushkin jeksys

Editors

#System Design Interview Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

##Basic Steps

User cases (description of sequences of events that, taken together, lead to a system doing something useful)
- Who is going to use it?
- How are they going to use it?

	// Taken from http://PSPDFKit.com. This snippet is under public domain.
	#define UIKitVersionNumber_iOS_7_0 0xB57
	BOOL PSPDFIsUIKitFlatMode(void) {
	static BOOL isUIKitFlatMode = NO;
	static dispatch_once_t onceToken;
	dispatch_once(&onceToken, ^{
	// We get the modern UIKit if system is running >= iOS 7 and we were linked with >= SDK 7.
	if (kCFCoreFoundationVersionNumber >= kCFCoreFoundationVersionNumber_iOS_7_0) {
	isUIKitFlatMode = (NSVersionOfLinkTimeLibrary("UIKit") >> 16) >= UIKitVersionNumber_iOS_7_0;
	}

	- (void)generateKeyPair:(NSUInteger)keySize {
	OSStatus sanityCheck = noErr;
	publicKeyRef = NULL;
	privateKeyRef = NULL;

	LOGGING_FACILITY1( keySize == 512 \|\| keySize == 1024 \|\| keySize == 2048, @"%d is an invalid and unsupported key size.", keySize );

	// First delete current keys.
	[self deleteAsymmetricKeys];

	@interface UIButton (VerticalLayout)

	- (void)centerVerticallyWithPadding:(float)padding;
	- (void)centerVertically;

	@end

	- (NSArray )tableView:(UITableView )tableView editActionsForRowAtIndexPath:(NSIndexPath *)indexPath {
	UITableViewRowAction moreAction = [UITableViewRowAction rowActionWithStyle:UITableViewRowActionStyleDefault title:@"More" handler:^(UITableViewRowAction action, NSIndexPath *indexPath){
	// maybe show an action sheet with more options
	[self.tableView setEditing:NO];
	}];
	moreAction.backgroundColor = [UIColor lightGrayColor];

	UITableViewRowAction blurAction = [UITableViewRowAction rowActionWithStyle:UITableViewRowActionStyleDefault title:@"Blur" handler:^(UITableViewRowAction action, NSIndexPath *indexPath){
	[self.tableView setEditing:NO];
	}];

	import Foundation

	/// An abstract class that makes building simple asynchronous operations easy.
	/// Subclasses must implement `execute()` to perform any work and call
	/// `finish()` when they are done. All `NSOperation` work will be handled
	/// automatically.
	open class AsynchronousOperation: Operation {

	// MARK: - Properties

	import Foundation

	extension Character {
	func utf8() -> UInt8 {
	let utf8 = String(self).utf8
	return utf8[utf8.startIndex]
	}
	}

	func encrypt(c:Character, key:Character) -> String {

	extension NSTimer {
	/**
	Creates and schedules a one-time `NSTimer` instance.

	- Parameters:
	- delay: The delay before execution.
	- handler: A closure to execute after `delay`.

	- Returns: The newly-created `NSTimer` instance.
	*/