[Android kotlin] lambda return statement and anonymous function

lambda The return statement in ： Returns... From a closed function

Use... In a normal loop return

Pass on to forEach Of lambda Use in return

If you are in the lambda Use in return keyword , He will From call lambda In a function that returns , Not just from lambda return . In this way return The statement is called Nonlocal return , Because it starts from a Ratio inclusion return A code block of returns... In a larger code block 了 . We can compare in java Medium for Circulation and synchronized Code block , Obviously, it will return... From the function

it is to be noted that Only in order to lambda Only when the function as a parameter is an inline function can it return from the outer function . Upper figure forEach Function body and lambda The function bodies of are inlined together , So when compiling, it is easy to return from the function containing it . In a non inline function lambda Use in return It's not allowed . A non inline function can pass to it lambda Save in variable , So that you can continue to use... After the function returns

from lambda return ： Use the tag to return

Can be in lambda Use local returns in expressions ,lambda The local return in is followed by for In the loop break The expression is similar . It will end lambda Implementation , And then call lambda Execute at the code of . Distinguish Partial return and Nonlocal return , Labels need to be used . From a lambda The expression returns, and you can mark it , And then in return The key word quote This tag

To mark a lambda expression , stay lambda Put a before the curly braces label name , Then put one @ Symbol . From one lambda return , stay return Put a... After the keyword @ Symbol , Add your signature

The other is to use lambda The function name of the function as a parameter can be used as a label , such as forEach

If you explicitly specify lambda The label of the expression , Reuse as a label has no effect , One lambda The number of labels in an expression cannot be more than one

Tagged this expression

If you bring the recipient lambda Specify the label , You can use the corresponding labeled this An expression accesses its implicit recipient

Anonymous functions ： The default is to use local return

Anonymous functions look similar to normal functions

Anonymous functions and ordinary functions have the same rules for specifying the return value type , Code block Anonymous functions require Explicitly specify the return type , If you use Expression function body Can Omit Return type

Anonymous function using expression function body

In anonymous functions , Without a label return Expressions are returned from anonymous functions , Instead of returning... From a function that contains an anonymous function .

The rules ：return From recent use fun The function declared by the keyword returns .lambda Not used fun keyword , therefore lambda Medium return Returns... From the outermost function , Anonymous functions use fun. Although anonymous functions look very similar to ordinary functions , But it's actually lambda Just another grammatical form of expression

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