V tem članku boste s primeri spoznali različne uporabniško določene funkcije, ki sprejemajo vnose različnih vrst in vrne izhodne podatke.
V prejšnjem članku Hitre funkcije smo spoznali funkcije. Zdaj si bomo ogledali različne načine in vrste, kako lahko v Swiftu ustvarimo funkcijo, to je obdelavo vhodnih in izhodnih podatkov v funkciji.
Funkcija brez parametra in brez povratne vrednosti
Te vrste funkcij ne sprejemajo nobene vhodne in povratne vrednosti.
func funcname () (// izjave) ALI func funcname () -> () (// izjave) ALI func funcname () -> Void (// izjave)
Vsa zgornja sintaksa velja za ustvarjanje funkcije, ki ne sprejme parametrov in ne vrne vrednosti.
Zgornja sintaksa func funcname() -> ()je tudi enakovredna, func funcname() -> Voidker Voidje le tipična oznaka (). Če želite izvedeti več, lahko obiščete Swift Typealias.
Primer 1: Niso bili posredovani nobeni parametri in ni vrnjene vrednosti
func greetUser() ( print("Good Morning!") ) greetUser()
Ko zaženete zgornji program, bo rezultat:
Dobro jutro!
Funkcija brez parametra, ampak z vrnjeno vrednostjo
Te vrste funkcij ne sprejemajo nobenih vhodnih parametrov, ampak vrnejo vrednost. Če želite dodati vrsto vrnitve, morate dodati puščico ( ->) in vrsto vrnitve.
func funcname () -> ReturnType (// stavki vrnejo vrednost)
Primer 2: Parametri niso bili posredovani, ampak vrnjena vrednost
func greetUser() -> String ( return "Good Morning!" ) let msg = greetUser() print(msg)
Ko zaženete zgornji program, bo rezultat:
Dobro jutro!
V zgornjem programu ste določili vrsto vrnitve kot String. Zdaj mora stavek vrniti niz iz stavka znotraj funkcije, sicer boste dobili napako.
returnključna beseda prenese nadzor programa iz telesa funkcije v klic funkcije. Če morate funkciji vrniti vrednost, dodajte vrednost za returnključno besedo.
return "Good Morning!"stavek vrne vrednost tipa Stringiz funkcije. Upoštevajte, da se morata vrsta vrnitve in vrednost ujemati.
Vrnitveno vrednost lahko dodelite tudi spremenljivki ali konstanti. let msg = dodeli vrnjeno vrednost konstanti msg. Izjava torej print(msg)oddaja Dobro jutro! v konzoli.
Če želite vrednost zanemariti, lahko preprosto uporabite _kot let _ =.
Funkcija s parametrom, vendar brez vrnjene vrednosti
Parametri se uporabljajo za vnos v funkcijo. Parameter vsebuje ime parametra in vrsto, ki ji sledi dvopičje ( :). Te vrste funkcij sprejmejo vhodni parameter, vendar ne vrnejo vrednosti.
func funcname (parameterName: Type) (// stavki)
Primer 3: Parametri so bili posredovani, vendar ni vrnjene vrednosti
func greetUser(msg:String) ( print(msg) ) greetUser(msg: "Good Morning!")
Ko zaženete zgornji program, bo rezultat:
Dobro jutro!
V zgornjem programu funkcija sprejema en sam parameter String. Parameter se lahko uporablja samo znotraj funkcije. msg je ime parametra.
Funkcijo lahko pokličete tako, da ji posredujete nizno vrednost z imenom parametra kot greetUser(msg: "Good Morning!"). Ime parametra sporočil je vidno samo znotraj funkcije greetUser().
Izjava torej print(msg)oddaja Dobro jutro! v konzoli.
Funkcija s parametrom in vrnjeno vrednostjo
Te vrste funkcij sprejmejo parametre in vrnejo vrednost.
func ime funkcije (ime parametra: vrsta) -> vrnitev (// stavki)
Primer 4: Parametri so posredovani in vrnejo vrednost
func greetUser(name:String) -> String ( return "Good Morning! " + name ) let msg = greetUser(name: "Jack") print(msg)
Ko zaženete zgornji program, bo rezultat:
Dobro jutro! Jack
V zgornjem programu funkcija sprejme en parameter tipa Stringin vrne tudi vrednost Dobro jutro! Jack tip String.
Funkcija z več parametri in več vrnjenimi vrednostmi
Te vrste funkcij zajemajo več parametrov, ločenih z vejico, in vrnejo tudi več vrednosti. V Swiftu lahko vrnete več vrednosti z uporabo Tuples. Če želite izvedeti več o tem, glejte Swift Tuples.
func funcname (ime-parametra: tip, ime-parametra2: tip,…) -> (vrnitev, vrnitev…) (// stavki)
Primer 5: Več posredovanih parametrov in večkratna vrnjena vrednost
func greetUser(name:String, age:Int) -> (String, Int) ( let msg = "Good Morning!" + name var userage = age if age < 0 ( userage = 0 ) return (msg, userage) ) let msg = greetUser(name: "Jack", age: -2) print(msg.0) print("You have (msg.1) coins left")
Ko zaženete zgornji program, bo rezultat:
Dobro jutro! Jack Ostalo ti je 0 kovancev
V zgornjem programu funkcija greetUser()sprejema več parametrov tipa Stringin Int. Funkcija vrne tudi več vrednosti kot nabor vrste Stringin Int.
Za dostop do vsake vrnjene vrednosti uporabimo položaje indeksa 0, 1, … Tu smo uporabili msg.0 za dostop do Dobro jutro! Jack in msg.1 za dostop do 0 .
Uporaba indeksnih položajev je včasih neintuitivna in neberljiva. To težavo lahko elegantno rešimo tako, da vrnemo vrednosti z imeni. Zgornji program je mogoče tudi napisati spodaj.
Example 6: Multiple return values with name
func greetUser(name:String, coins:Int) -> (name:String, coins:Int) ( let msg = "Good Morning!" + name var userCoins = coins if coins < 0 ( userCoins = 0 ) return (msg, userCoins) ) let msg = greetUser(name: "Jack",coins: -2) print(msg.name) print("You have (msg.coins) coins left")
In this program, the return type is of tuple that contains the variable name with the type. The main advantage of this is you can access the result using the variable name as msg.name and msg.coins instead of msg.0 and msg.1.
Function with argument label
When you define a function that accepts inputs, you can define the input name with the help of parameter name. However, there is another type of name which you can give along with the parameter name, known as argument label.
The use of argument labels allow a function to be called in an expressive way, sentence-like manner, while still providing a function body that is readable and clear in intent.
Each function parameter has both an argument label and a parameter name. By default, parameters use their parameter name as their argument label. But, if you explicitly define the argument name, the argument label is used when calling the function.
The syntax of function with argument label is
func funcname(argumentLabel parameterName:Type)-> Return Type ( //statements )
Let's see this in example below.
Example 7: Function without argument label
func sum(a:Int, b:Int) -> Int ( return a + b ) let result = sum(a: 2, b: 3) print("The sum is (result)")
When you run the above program, the output will be:
The sum is 5
In the above example, we have not specified the argument label, so it takes default parameter name a and bas the argument label while calling the function.
You may notice the function call is not expressive/sentence when calling the function. You may think it can be made more expressive as English if you could make the function call as:
let result = sum(of: 2, and: 3)
Now let's change the function as:
Example 8: Function with better function call but not as parameter names
func sum(of:Int, and:Int) -> Int ( return of + and ) let result = sum(of: 2, and: 3) print("The sum is (result)")
Now the method call is expressive. However, now we have to use the parameter name of & and in return of + and to find the sum of two numbers. Now, this makes the function body unreadable. Use of a and b instead of of&and would make more sense inside the function body.
For this purpose we have to explicitly define argument label as:
Example 9: Function with argument labels
func sum(of a :Int, and b:Int) -> Int ( return a + b ) let result = sum(of: 2, and: 3) print("The sum is (result)")
In the above program, the function accepts two parameter of type Int. The function call uses the argument label of & and which makes sense while calling the function as sum(of: 2, and: 3) instead of sum(a: 2, b: 3).
Also, the function body uses the parameter name a and b instead of of & and which also makes more sense while applying operations.
You can also omit the argument label by writing a _ before the parameter name.
func sum(_ a :Int, _ b:Int) -> Int ( return a + b ) let result = sum(2, 3) print("The sum is (result)")
Function with default parameter values
You can give default values for any parameter in a function by assigning a value to the parameter after that parameter's type. Giving a default parameter allows you to neglect the parameter while calling the function.
If you do not pass value to the parameter while calling the function, its default value is used. However, if you explicitly pass a value to the parameter while calling, the specified value is used.
func funcname(parameterName:Type = value) -> Return Type ( //statements )
Example 10: Function with default parameter values
func sum(of a :Int = 7, and b:Int = 8) -> Int ( return a + b ) let result1 = sum(of: 2, and: 3) print("The sum is (result1)") let result2 = sum(of: 2) print("The sum is (result2)") let result3 = sum(and: 2) print("The sum is (result3)") let result4 = sum() print("The sum is (result4)")
When you run the above program, the output will be:
The sum is 5 The sum is 10 The sum is 9 The sum is 15
In the above program, the function sum(of a :Int = 7 , and b:Int = 8) -> Int accepts two parameter of type Int but also specifies the default value of parameter a = 7 and b = 8.
If you pass value as a parameter in the function call as sum(of: 2, and: 3) then 2 and 3 is used instead of parameter default value.
But if you don't pass the parameter value as sum() , then default value 7 and 8 are used as the parameter value.
Function with variadic parameters
A variadic parameter can accept zero or more values of a specific type. You can specify variadic parameter by inserting three period characters (… ) after the parameter's type name.
You usually use a variadic parameter when you need to pass a varying number of input values to the parameter when the function is called. For example, a list of numbers, a list of alphabets, etc.
The syntax of function with variadic parameters is:
func funcname(parameterName:Type… ) -> Return Type ( //statements )
Example 11: Function with variadic parameters
func sum(of numbers:Int… ) ( var result = 0 for num in numbers ( result += num ) print("The sum of numbers is (result)") ) sum(of: 1, 2, 3, 4, 5, 6, 7, 8)
In the above program, the function sum(of numbers:Int… ) accepts a variadic parameter of type Int. A variadic parameter can accept multiple values separated by comma as sum(of: 1, 2, 3, 4, 5, 6, 7, 8).
The values 1, 2, 3, 4, 5, 6, 7, 8 passed as a variadic parameter are made available within the function's body as an array of the Int type. Therefore, we can apply for-in loop in the value as for num in numbers.
When you run the above program, the output will be:
The sum of numbers is 36
Note: Swift built in print() function also accepts variadic parameter of type Any.
Any represents to any data type in Swift e.g. Int, Float, Double,String etc.
Function with in-out parameters
When you define the function parameter, the function parameters cannot be modified inside the body. So they are constants by default. Let's see this in example:
func process(name:String) ( if name == ""( name = "guest" ) )
The above program results a compile-time error because you cannot change the value of a parameter.
If you want a function to modify a parameter's value, you need to define the parameter as in-out parameter. You write an in-out parameter by placing the inout keyword right before a parameter's type.
Behind the scenes, an in-out parameter has a value that is passed into the function, is modified by the function, and is passed back out of the function to replace the original value. Therefore the value passed in the function call cannot be a constant. You must declare it as a variable.
The syntax of function with inout parameter is:
func funcname(parameterName:inout Type) -> Return Type ( //statements )
Example 12: Function with in out parameter
func process(name:inout String) ( if name == ""( name = "guest" ) ) var userName = "" process(name: &userName) print(userName)
When you run the above program, the output will be:
guest
In the above program, we have declared a function that accepts inout parameter name so that the parameter can be changed/altered inside the body of the function.
You must use ampersand (&) sign directly before a variable's name when you pass argument to an in-out parameter so that it can be modified by the function.
