This is the sixth day of my participation in the November Gwen Challenge. Check out the event details: The last Gwen Challenge 2021
The introduction
When I started to write Swift code, it was always not concise and did not give full play to the characteristics of Swift. As the writing went on, I also summarized some Swift development tips to make the code look more concise and elegant.
Content is divided into two articles, we first look at the first ~
Using built-in functions
Now we have an array of integers, and we want to add up all the numbers in the array. Your first reaction might be a for loop, so you write the following code:
let numbers = [2021.11.12]
var sum = 0
for number in numbers {
sum + = number
}
print(sum) / / 2044
Copy the codeThere’s nothing wrong with this, of course, but we can use reduce(_:_:) to simplify the for loop to a single line:
let numbers = [2021.11.12]
let sum = numbers.reduce(0.+)
print(sum) / / 2044
Copy the codeThis is equivalent to 0 + 2021 + 11 + 12 reduce. The first argument, 0, is the initial value, which is equivalent to var sum = 0 in the for loop above. The second argument accepts a closure, which gives us the opportunity to do whatever we want inside the closure.
In addition to reduce(_:_:), Swift provides other built-in functions such as filter(_:), map(_:), flatMap(_:), firstIndex(Where :), and more. Command + Shift +0 opens the development document for more information.
Omit the return keyword
If a function or closure has only one line of code, you can omit the return keyword. And, if you prefer, you can put all the code on one line:
func makeGreeting(withName name: String) -> String {
"Ask for a thumbs up,\(name)"
}
func makeGreeting(withName name: String) -> String { "Ask for a thumbs up,\(name)" }
Copy the codeSimplify the closure
struct Person {
var name: String
var age: Int
.
}
Copy the codeSelect Persons older than 18 from Persons array filter(_:);
let person1 = Person(name: "JieJie", age: 20)
let person2 = Person(name: "Faker", age: 25)
let person3 = Person(name: "JakeyLove", age: 30)
let person4 = Person(name: "JinX", age: 10)
let persons = [person1, person2, person3, person4]
let result = persons.filter { person in
person.age > 18
}
print(result.map{ $0.name }) //["JieJie", "Faker", "JakeyLove"]
Copy the codeSwift automatically provides parameter name abbreviations for inline functions, so the above filter statement can be simplified to:
let result = persons.filter{ $0.age > 18 }
Copy the codeCheck if the array is out of bounds
If you draw persons and the number of persons is not 6, extend the drawing date, you might do this:
let index = 6
if index > = 0 && index < persons.count {
print("Congratulations\(persons[index].name)The winning")}else {
print("Extension of Lucky Draw Date")}Copy the codeThe indices property for arrays is used to make it bigger:
if persons.indices.contains(index) {
print("Congratulations\(persons[index].name)The winning")}else {
print("Extension of Lucky Draw Date")}Copy the codeThe default value
Everyone knows you can use?? Set defaults for optional variables. In Swift, there are more places to set defaults, such as:
- Set default values for function parameters
- Set a default value for a key in the dictionary
Let’s start by setting the default value for a function parameter, which can be omitted when called:
func greet(name: String = "World") -> String {
"Hello,\(name)"
}
greet("World!!!") //Hello,World!!!
greet() //Hello,World
Copy the codeLet’s look at setting a default value for a key in a Dictionary.
Suppose we have a Names array that contains names of people, and now we write a function that returns the names that occur the most. One way to do this is as follows:
let names = ["Zhang"."Xiao li"."Zhang"."Xiao li"."Zhang"."Wang"]
func findMostCountName(inNames names: [String]) -> String {
var occurrenceFor: [String : Int] = [:]
for name in names {
if let count = occurrenceFor[name] {
occurrenceFor[name] = count + 1
} else {
occurrenceFor[name] = 1}}var maxCount = 0
var result = ""
for (name, count) in occurrenceFor {
if count > maxCount {
maxCount = count
result = name
}
}
return result
}
let name = findMostCountName(inNames: names)
print(name) / / zhang
Copy the codeLet’s look at the default value for dictionary: occurrenceFor’s key:
func findMostCountName(inNames names: [String]) -> String {
var occurrenceFor: [String : Int] = [:]
for name in names {
occurrenceFor[name, default: 0] + = 1 // If the key exists, return the corresponding value; Otherwise return 0
}
var maxCount = 0
var result = ""
for (name, count) in occurrenceFor {
if count > maxCount {
maxCount = count
result = name
}
}
return result
}
Copy the codeAs you can see, setting default values for the Dictionary key makes your code look cleaner. Replace the if-else statement with a single line of code.
Check if the variable is between two numbers
If you have a field: age, now determine if it is between 18 and 32. Here’s what we usually do:
let age = 23
if age > = 18 && age < = 32 {
print("Fit the bill")}Copy the codeYou might think there’s nothing wrong with writing like this, but look at this:
let age = 23
if age < = 18 && age > = 32 {
print("Fit the bill")}Copy the codeIsn’t that true, but the print statement will never execute. How do you feel when you read these two if statements? Do you need to have a pause in your brain to think about whether or not you fit the criteria? This makes it unreadable and error-prone.
Swift provides a more readable and easy way to:
let age = 23
if (18.32).contains(age) {
print("Fit the bill")}if (18.32) ~ = age {
print("Fit the bill")}Copy the codeconclusion
- Use built-in functions instead of for loops whenever possible
- One-line functions omit the return keyword
- Closure simplification
- Check for array out-of-bounds methods
- Provide default values for function parameters and dictionary keys
- Check if the variable is between two numbers
That’s all for today’s tip. You might as well practice it in your project if you think it’s useful