Explain how bitcode works

https://jonasdevlieghere.com/embedded-bitcode/ Bitcode is the intermediate representation used by the LLVM compiler and contains all the information required to recompile an application. Having the bitcode present, in addition to machine code, Apple can further optimize applications by compiling and linking specifically for the user's target device. This is one approach to app thinning, which aims to achieve smaller binaries and therefore more free space on your iDevice. It will most likely replace Apple's current approach, where a developer uploads a fat binary to the App Store, which contains machine code for each target architecture.

How to find files that were updated in the past 24 hours

 sudo find / -type f -ctime 0

How to create abstract functions in Swift

 class BaseClass {

    func abstractFunction() {
        preconditionFailure("This method must be overridden") 
    } 
}

class SubClass : BaseClass {
     override func abstractFunction() {
         // Override
     } 
}

https://stackoverflow.com/questions/24110362/abstract-functions-in-swift-language

Get Value For Selector

func getValueForSelector(cls: AnyClass, selector: Selector) -> AnyObject {

  let method = class_getInstanceMethod((cls), selector)!

  let methodIMP : IMP! = method_getImplementation(method)

  let newAmountObj = unsafeBitCast(methodIMP,to:(@convention(c)(AnyClass?,Selector,Any?)->Any).self)(cls,selector, nil) as AnyObject

  return newAmountObj

}

Accessor Search Patterns

Search Pattern for the Basic Setter

The default implementation of setValue:forKey:, given key and value parameters as input, attempts to set a property named key to value (or, for non-object properties, the unwrapped version of  value, as described in Representing Non-Object Values) inside the object receiving the call, using the following procedure:

1. Look for the first accessor named set<Key>: or _set<Key>, in that order. If found, invoke it with the input value (or unwrapped value, as needed) and finish.

2. If no simple accessor is found, and if the class method accessInstanceVariablesDirectly returns YES, look for an instance variable with a name like _<key>, _is<Key>, <key>, or is<Key>, in that order. If found, set the variable directly with the input value (or unwrapped value) and finish.

3. Upon finding no accessor or instance variable, invoke setValue:forUndefinedKey:. This raises an exception by default, but a subclass of NSObject may provide key-specific behavior.

3 ways to call ObjC methods from swift

 There are three ways to dynamically call the method in this class:

1. Using performSelector()

let selector = NSSelectorFromString("titleForItem:withTag:")
let unmanaged = toolbar.perform(selector, with: "foo", with: "bar")
let result = unmanaged?.takeRetainedValue() as? String

2. Using methodForSelector() with @convention(c)

typealias titleForItemMethod = @convention(c)
    (NSObject, Selector, NSString, NSString) -> NSString
  
let selector = NSSelectorFromString("titleForItem:withTag:")
let methodIMP = toolbar.method(for: selector)
let method = unsafeBitCast(methodIMP, to: titleForItemMethod.self)
let result = method(toolbar, selector, "foo", "bar")

3. Using NSInvocation

It's only available in Objective-C.

SEL selector = @selector(titleForItem:withTag:);
NSMethodSignature *signature = [toolbar methodSignatureForSelector:selector];

NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
invocation.target = toolbar;
invocation.selector = selector;

NSString *argument1 = @"foo";
NSString *argument2 = @"bar";
[invocation setArgument:&argument1 atIndex:2];
[invocation setArgument:&argument2 atIndex:3];

[invocation invoke];

NSString *result;
[invocation getReturnValue:&result];

Or, we can use Dynamic 🎉

let result = Dynamic(toolbar)            // Wrap the object with Dynamic
    .titleForItem("foo", withTag: "bar") // Call the method directly!

More details on how the library is designed and how it works here.

Calling selectors using Dynamic library

let result = Dynamic(toolbar)            // Wrap the object with Dynamic
    .titleForItem("foo", withTag: "bar") // Call the method directly!

 https://github.com/mhdhejazi/Dynamic

https://github.com/mhdhejazi/Dynamic/blob/master/Tests/DynamicTests/DynamicTests.swift

invoke objective c function using selectors

 https://github.com/mhdhejazi/Dynamic

How to call methods using selectors

func getClass(_ classNameString: String) -> AnyClass {

  let clazz = objc_getMetaClass(classNameString)

  return clazz as! AnyClass

}

func callMethod2(clazz: AnyClass, method: String) -> AnyObject {

  let selector : Selector = NSSelectorFromString(method)

  let method = class_getInstanceMethod((clazz), selector)!

  let methodIMP : IMP! = method_getImplementation(method)

  let newAmountObj = unsafeBitCast(methodIMP,to:(@convention(c)(AnyClass?,Selector,Any?)->Any).self)(clazz,selector, nil) as AnyObject

  return newAmountObj

}

func callMethod(clazz: AnyClass, method: String) -> AnyObject? {

  let selector : Selector = NSSelectorFromString(method)

  guard let method = class_getClassMethod((clazz), selector) else { return nil }

  let methodIMP : IMP! = method_getImplementation(method)

  let newAmountObj = unsafeBitCast(methodIMP,to:(@convention(c)(AnyClass?,Selector,Any?)->Any).self)(clazz,selector, nil) as AnyObject

  return newAmountObj

}

func callMethod(classNameString: String, method: String) -> AnyObject? {

  let clazz: AnyClass = getClass(classNameString)

  let newAmountObj = callMethod(clazz: clazz, method: method)

  return newAmountObj

}

Dealing with managed and unmanaged objects

While most CoreFoundation APIs have been annotated, some significant chunks have yet to receive attention. As of this writing, the Address Book framework seems the highest profile of the unannotated APIs, with several functions taking or returning Unmanaged-wrapped types.

An Unmanaged<T> instance wraps a CoreFoundation type T, preserving a reference to the underlying object as long as the Unmanaged instance itself is in scope. There are two ways to get a Swift-managed value out of an Unmanaged instance:

• takeRetainedValue(): returns a Swift-managed reference to the wrapped instance, decrementing the reference count while doing so—use with the return value of a Create Rule function.

• takeUnretainedValue(): returns a Swift-managed reference to the wrapped instance without decrementing the reference count—use with the return value of a Get Rule function.

 https://nshipster.com/unmanaged/

 

converting an unmanaged object to a string

 https://vandadnp.wordpress.com/2014/07/07/swift-convert-unmanaged-to-string/

how to get a certificate in java

 http://littlesvr.ca/grumble/2014/07/21/android-programming-connect-to-an-https-server-with-self-signed-certificate/

Merge dictionaries in Swift

Keep the current value (value in dictionary1) if there is a duplicate key 

dictionary1.merge(dictionary2) {(current,_) in current}

Keep the new value (value in dictionary2) if there is a duplicate key 

dictionary1.merge(dictionary2) {(_,new) in new}

 https://www.tutorialkart.com/swift-tutorial/merge-dictionaries-in-swift/

Convert Any object to a String

String(describing: someValue)

How to reset the scroll back buffer on a Mac terminal via command line

printf '\033[2J\033[3J\033[1;1H'

iOS framework stuff

https://www.bignerdranch.com/blog/it-looks-like-you-are-trying-to-use-a-framework/

regex validation

https://regex101.com

c++ switch Vs hash map optimization

• cost(Hash_table) >> cost(direct_lookup_table)
• cost(direct_lookup_table) ~= cost(switch) if your compiler translates switches into lookup tables. 
• cost(switch) >> cost(direct_lookup_table) (O(N) vs O(1)) if your compiler does not translate switches and use conditionals, but I can't think of any compiler doing this.
• But inlined direct threading makes the code less readable.

https://stackoverflow.com/questions/931890/what-is-more-efficient-a-switch-case-or-an-stdmap

Easy explanation of stack views

https://nshipster.com/uistackview/

Lunux shell script samples

https://www.ubuntupit.com/simple-yet-effective-linux-shell-script-examples/