The Let,apply,with,run function difference of Kotlin

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Kotlin's Let,apply,with,run function difference rearrangement

Rearrange the differences between the various functions, please go here.

void below

For a long time have been using the Kotlin language, but also purely using simple syntax, and recently sometimes written code, the editor automatically prompts to use let and other functions, and then dedicated to spend a little time to study the next.

Let

First let () is defined as the default current object as the IT parameter of the closure, the return value is the last line inside the function, or the specified return

fun <T, R> T.let(f: (T) -> R): R = f(this)

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Simple example:

fun testLet ( ): Int {//fun <t, r> t.let< Span class= "Hljs-params" > (f: (T) R): r {f (this"} "testlet".  Let {println (IT) println (IT) println (IT) return 1}}//Run result//testlet//testlet// Testlet                

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You can look at the last generated class file, the code is formatted, and the compiler just adds the contents of let behind our original variable.

public static final int testLet() {    String str1 = "testLet"; String it = (String)str1; int $i$a$1$let; System.out.println(it); System.out.println(it); System.out.println(it); return 1;}

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Come up with some complicated examples.

fun testLet ( ): Int {//fun <t, r> t.let< Span class= "Hljs-params" > (f: (T) R): r {f (this"} "testlet".  Let {if  (Random (). Nextboolean ()) { Println (IT) return 1} else {println (IT) return 2}}}     

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The compiled class file

public Span class= "Hljs-keyword" >static final int testlet () {String str1 =  "Testlet"; String it = (string) str1; int $i $a$1$let; if (new Random (). Nextboolean ()) {System. OUT.PRINTLN (IT); return 1;} System. out.println (IT); return 2;}         

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Apply

The Apply function calls the Apply function of an object, and within the scope of the function, any method of the object can be called, and the object is returned

fun <T> T.apply(f: T.() -> Unit): T { f(); return this }

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code example

Fun testapply () {Fun <T> t.apply(F:t. (), Unit):R =F();ReturnThis}arraylist<String>().apply {add (  "testapply") add ( "testapply") add ( "testapply") println ( "this =" + this)}. let {println (IT)}}//run result//this = [testapply, testapply, testapply]//[testapply, testApply, testapply]             

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The compiled class file

  PublicStaticfinal void Testapply () {ArrayList LocalArrayList1 =new ArrayList (); ArrayList localArrayList2 = (ArrayList) localArrayList1; int  $i  $a $1  $apply; ArrayList  $receiver;  $receiver. Add ( "testapply");  $receiver. Add ( "testapply");  $receiver. Add ( "testapply"); String str =  "this =" +  $receiver; System.out.println (str); LocalArrayList1 = LocalArrayList1; ArrayList it = (ArrayList) localArrayList1; int  $i  $a $2  $let; SYSTEM.OUT.PRINTLN (IT); } 

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With

The WITH function is a separate function, not a extension in Kotlin, so the calling method is a bit different, the return is the last line, and then you can call the object's methods directly, feeling like a combination of let and apply.

with(receiver: T, f: T.() -> R): R = receiver.f()

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code example:

Fun Testwith () {Fun <t, r>With(Receiver:t, F:t. () R):R =Receiver.F()with (arraylist<string> ()) { Add ( "Testwith") add (" Testwith ") add ( Span class= "hljs-string" > "Testwith") println (" this = "+ this)}. let {println (IT)}}//run result//this = [testwith, testwith, testwith]//kotlin. Unit                 

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class file

 PublicStaticfinal void Testwith () {Object Localobject =new ArrayList (); ArrayList LocalArrayList1 = (ArrayList) localobject; int  $i  $a $1  $with; ArrayList  $receiver;  $receiver. Add ( "Testwith");  $receiver. Add ( "Testwith");  $receiver. Add ( "Testwith"); String str =  "this =" +  $receiver; System.out.println (str); Localobject = unit.instance; Unit it = (unit) Localobject; int  $i  $a $2  $let; SYSTEM.OUT.PRINTLN (IT); } 

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Run

The run function is much like the Apply function, except that the run function uses the return of the last line, and apply returns the current object.

fun <T, R> T.run(f: T.() -> R): R = f()

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code example

fun TestRun ( {//fun <t, r> t.run (f:t. () R): r = f () " testrun ". run {println (  "this =" + this)}. let {println (IT)}}//run result//this = testrun//kotlin. Unit                 

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class file

  public static finalvoid TestRun () {Object localobject="TestRun";String str1= (String) Localobject; Int $i  $a $1  $run; string  $receiver; string str2 =  "this =" +  $receiver; System.out.println (str2); localobject = unit= (unit) localobject; int  $i  $a $2 $let; System.out.println (it);       

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Summarize

How, is not looking dizzy, it's okay, let's summarize.

Name of function	definition	Parameters	return value	extension	other
Let	Fun T.let (f: (T), R): R = f (This)	It	Closed Packet return	Is
Apply	Fun t.apply (F:t (), Unit): T {f (); return this}	None, you can use this	This	Is
With	Fun with (Receiver:t, F:t. () R): R = RECEIVER.F ()	None, you can use this	Closed Packet return	Whether	Call mode differs from other
Run	Fun T.run (f:t. () R): R = f ()	None, you can use this	Closed Packet return	Is

Let,apply,with,run function Difference of kotlin (RPM)