This is the 11th day of my participation in the Gwen Challenge in November. Check out the details: The last Gwen Challenge in 2021

preface

Kotlin’s built-in functions are available in Kotlin for extensions and easy coding for developers. Can greatly improve the “development efficiency”. Today, I will mainly explain:

  • Let the function
  • The braking function
  • With the function
  • The run function
  • The apply function

I. Let function

Method of use

Let {it.todo()} // Function 1: use it instead of object to access its public attribute & method Object.let {it.todo()} .todo()}.todo()}.todo() {.todo()Copy the code

Use the sample

// Use Java if(mVar! = null ){ mVar.function1(); mVar.function2(); mVar.function3(); } // use kotlin (no let function) mVar? .function1() mVar? .function2() mVar? .function3() // use kotlin (use let function) // to facilitate the same null processing & determine the scope of the mVar variable mVar? .let { it.function1() it.function2() it.function3() }Copy the code

2. Also function

Functions & Application scenarios

Similar to let, except that the return value is:

  • Let function: return value = last line/return expression
  • Also function: Returns the value = itself of the object passed in

Use the sample

// let function var result = mvar.let {it.function1() it.function2() it.function3() 999 Var result = mvar.also {it.function1() it.function2() it.function3() 999Copy the code

The with function

role

When calling multiple methods/attributes of the same object, you can directly invoke the method name/attribute without the object name duplication

Application scenarios

Multiple methods/properties of the same object need to be called

Method of use

with(object){ // ... } // Return value = the last line of the function block/return expressionCopy the code

Use the sample

// kotlin val people = people (" Carson ", 25) with(people) {println("my name is $name, I am $age years old") } // Java User peole = new People("carson", 25); String var1 = "my name is " + peole.name + ", I am " + peole.age + " years old"; System.out.println(var1);Copy the code

The run function

Functions & Application scenarios

Combined with the functions of let and with, namely:

  1. When calling multiple methods/attributes of the same object, you can directly invoke the method name/attribute without the object name duplication
  2. Defines a variable in a particular scope
  3. Do a unified short processing

Method of use

object.run{ // ... } // Return value = the last line of the function block/return expressionCopy the code

Use the sample

// kotlin val people = people (" Carson ", 25) people? .run{ println("my name is $name, I am $age years old") } // Java User peole = new People("carson", 25); String var1 = "my name is " + peole.name + ", I am " + peole.age + " years old"; System.out.println(var1);Copy the code

5. Apply function

Functions & Application scenarios

This is similar to the run function, except that the return value is:

  • The run function returns the value/expression of the last line
  • The apply function returns the object itself passed in

Application scenarios

Object instance initialization requires the assignment of properties in the object & return the object

Use the sample

// run function val people = people (" Carson ", 25) val result = people? .run{ println("my name is $name, I am $age years old") I am $age years old") I am $age years old Run {println("my name is $name, I am $age years old") 999}} val result = people?Copy the code

conclusion

Above are the functions, application scenarios and usage methods of several kotlin built-in functions. The following are briefly summarized:

If you do not understand, you can leave a message, the official website also has a detailed introduction