Memorize

This is the first project of Stanford CS193p spring quarter 2020.

This is my personal follow up of the lectures and assignments, which are now open to the public.

Lecture 1

Computed properties

Struct's or class' property that is calculated on access. In the next example, body is a calculated property:

struct ContentView: View {
    var body: some View {
        Text("Hello, World!")
    }
}

In this case body is a read-only calculated property.

See:

• Properties

"some" keyword

The some keyword is used to indicate that a value has an opaque type.

See:

• Opaque types
• The "Some" Keyword In Swift

Lecture 2

MVVM

Model-View-ViewModel

Model: should be UI independant (data + logic). Model structs or classes should not import SwiftUI, for example. It's the source of truth regarding the state of the application.

View: should reflects the Model. The data should flow from the Model to the View and not the other way (not really true). View should be stateless and its desired to be declarative. It should be reactive to the model, every time the Model changes the View needs to update.

ViewModel: binds the Model to the View. It might do some interpretation of the Model data and prepare it for the View. Tries to notice changes in the model. Publish the model changes so the Views can notice them, but does not inform any View directly, the Views are the ones that subscribe to the ViewModel. It process intent, that intent is the user intent to change the model. That intent processing might end in a modification of the model.

Types

Struct and class

Both have properties. Properties can be stored, which can be contants or variables (let and var), and computed.

Both can have functions. There's a special function called init, an initializer, like a constructor. Actually a struct or class can have many initializers, each one with different parameters.

struct	class
value type	reference type
copied when passed	passed via "pointers"
copy on write	reference counted
functional programming	object oriented programming
no inheritance	single inheritance
"free" init initialize all vars	"free" init initialize no vars
mutability must be explicit (var)	always mutable

See:

• Structures and Classes

Generics

See:

• Generics

Functions as types

See:

• Functions
• Clousures

Lecture 3

Protocols

Protocols are similar to Java interfaces, but properties can also be included to its definition.

It's also possible to add defaut implementations of functions via extensions.

See:

• Protocols

Extensions

Extensions let us:

• Add new functions implementations to classes and structs.
• Add default implementations to protocols functions.
• Make a struct or class conform to a protocol.

Example of the last case:

struct Boat {
	...
}

...

extension Boat: Moveable {
	// implement Moveable's functions and properties
}

In the example, Boat didn't conform to Moveable protocol, but then, maybe in another source file or even another project, we decided that Boat should conform to Moveable protocol, so we implement the corresponding functions and properties, using the corresponding syntax, and now Boat does conform to the protocol.

See:

• Extensions

Generics, protocols & extensions

With protocols and extensions we can extend structs and classes capabilities that use generics given that the generic types conforms to a given protocols. This is a powerful feature not usually seen in other languges.

Example: Array is a struct that is defined using generics. We can use protocols and extensions capabilities to define the following function:

extension Array where Element: Identifiable {
    func firstIndex(matching: Element) -> Int? {
        for index in 0..<self.count {
            if matching.id == self[index].id {
                return index
            }
        }
        return nil
    }
}

That will extend Array capabilities, so now we can find the first index of an element in an array that has the same id of the element passed in the argument, given that both the array's elements and the one in the argument conforms to the Identifiable protocol.

See:

• Generics

Layout

Lecture 4

Enums

See:

• Enumerations

Optionals

See:

• The Basics (Optionals part specifically)
• Optional Chaining