1,a single statement can be broken into multiple lines ,For example, after an opening parenthesis is a good place:
print(
"world")
2,Swift is a compiled language， the syntax of message-sending is dot-notation. every noun is an object, and every verb is a message.
3,An object type can be extended in Swift, meaning that you can define your own messages on that type. For example, you can’t normally send the say- Hello message to a number. But you can change a number type so that you can:
extension Int {
func sayHello() {
print("Hello, I'm (self)")
}
}
1.sayHello() // outputs: "Hello, I'm 1"
4, what “everything is an object” really means. ?
In Swift, then, 1 is an object. In some languages, such as Objective-C, it clearly is not; it is a “primitive” or scalar built-in data type. So the distinction being drawn here is between object types on the one hand and scalars on the other. In Swift, there are no scalars; all types are ultimately object types. That’s what “everything is an object” really means.
Swift has three kinds of object type: classes, structs, and enums.
5，Variables : A variable is a name for an object. Technically, it refers to an object;
let one =1
var two = 2
one = two //compile error
The two kinds of variable declaration differ in that a name declared with let cannot have its value replaced. A variable declared with let is a constant; its value is assigned once and stays.
Variables literally have a life of their own — more accurately, a lifetime of their own. As long as a variable exists, it keeps its value alive.
6,Functions : A function is a batch of code that can be told, as a batch, to run.
7，A namespace is a named region of a program.
8，The top-level namespaces are modules.
9. self. an instance needs a way of sending a message to itself. This is made possible by the magic word self.
It turns out that every use of the word self I’ve just illustrated is completely optional. You can omit it and all the same things will happen 。
The reason is that if you omit the message recipient and the message you’re sending can be sent to self, the compiler supplies self as the message’s recipient under the hood.
10，private: Supose I want a Dog instance itself to be able to change self.whatADogSays. Then whatADogSays has to be a var; otherwise, even the instance itself can’t change it. Also, suppose I don’t want any other object to know what this Dog says, except by calling bark or speak. Even when declared with let, other objects can still read the value of whatADogSays. Maybe I don’t like that. To solve this problem, Swift provides the private keyword.
11，If you’re ignoring a function call result deliberately, you can silence the compiler warning by assigning the function call to _ (a variable without a name) — for example, _ = sum(4,5). Alternatively, if the function being called is your own, you can prevent the warning by marking the function declaration with @discardableResult.
12，Function Signature ：(Int, Int) -> Int 。A function’s signature is, in effect, its type — the type of the function. The signature of a function must include both the parameter list (without parameter names) and the return type, even if one or both of those is empty;
13,
func echo(string s:String, times n:Int) -> String {
var result = ""
for _ in 1...n { result += s}
return result
}
In the body of that function, there is now no times variable available; times is purely an external name, for use in the call. The internal name is n, and that’s the name the code refers to.
14, Default Parameter Values : To specify a default value in a function declaration, append = and the default value after the parameter type:
class Dog {
func say(_ s:String, times:Int = 1) {
for _ in 1...times {
print(s)
}}
}
15, To indicate in a function declaration that a parameter is variadic, follow it by three dots, like this:
func sayStrings(_ arrayOfStrings:String ...) {
for s in arrayOfStrings { print(s) }
}
16, The default separator: (for when you provide multiple values) is a space, and the default terminator: is a newline; you can change either or both:
print("Manny", "Moe", separator:", ", terminator:", ")
print("Jack")
// output is "Manny, Moe, Jack" on one line
17, Modi able Parameters ,In the body of a function, a parameter is essentially a local variable. By default, it’s a variable implicitly declared with let.
You can’t assign to it
func say(_ s:String, times:Int, loudly:Bool) {
loudly = true // compile error
}
If your code needs to assign to a parameter name within the body of a function, declare a var local variable inside the function body and assign the parameter value to it;
func removeCharacter(_ c:Character, from s:String) -> Int {
var s = s
var howMany = 0
while let ix = s.characters.index(of:c) {
s.remove(at:ix)
howMany += 1 }
return howMany
}
this change didn’t affect the original string
If we want our function to alter the original value of an argument passed to it, we must do the following:
-
The type of the parameter we intend to modify must be declared inout.
-
When we call the function, the variable holding the value we intend to tell it to
modify must be declared with var, not let.
-
Instead of passing the variable as an argument, we must pass its address. This is
done by preceding its name with an ampersand (&). Our removeCharacter(_:from:) now looks like this:
-
-
func removeCharacter(_ c:Character, from s: inout String) -> Int { var howMany = 0while let ix = s.characters.index(of:c) { s.remove(at:ix)howMany += 1 }
return howMany }
-
let c = UIColor.purple
var r : CGFloat = 0
var g : CGFloat = 0
var b : CGFloat = 0
var a : CGFloat = 0
c.getRed(&r, green: &g, blue: &b, alpha: &a)
func popoverPresentationController(
_ popoverPresentationController: UIPopoverPresentationController,
willRepositionPopoverTo rect: UnsafeMutablePointer<CGRect>,
in view: AutoreleasingUnsafeMutablePointer<UIView>) {
view.pointee = self.button2
rect.pointee = self.button2.bounds
}