Programming in Scala (Second Edition) reading notes 6 functions and closures

When programs get larger, you need some-to divide-them into smaller,

More manageable pieces. For dividing up control flow, Scala offers a approach familiar to all experienced programmers:divide the code into FUNCT Ions. In fact, Scala offers several ways to define functions that is not

Present in Java. Besides methods, which is functions that IS members

Of some object, there is also functions nested within functions, function literals, and function values. This chapter takes to a tour through all of

These flavors of functions in Scala

Generalizing's programming idea

A variety of ways to create functions

1. The most common-define a function is as a member of some object.

Such a function is called a method

Define a function by defining a method inside an object

2. Define the function in the body of the function, which is the local function

You can define functions inside and other functions. Just like local variables, such local functions is visible only in their enclosing block

The local function is visible only within the function closure in which it resides

3. Anonymous functions, or called function literals

val cubic = (x:int) + x * x * x

4. Ignore parameter types

Val nums = list (1,2,3,4,5)//> nums:list[int] = List (1, 2, 3, 4, 5) Nums.filter ((x) = x > 2) > Res0:list[int] = List (3, 4, 5)

5. Continue simplifying with placeholder

Val nums = list (1,2,3,4,5)//> nums:list[int] = List (1, 2, 3, 4, 5) Nums.filter (_ > 2) > Res0:list[int] = List (3, 4, 5)

Val F = (_: Int) + (_: int)//> f: (int, int) + int = <function2>

6. Partial function (patially applied functions)

Consider a scenario in which a function f has been defined, which accepts 5 parameters. When used, it is found that 2 parameters are always fixed. Then there is no simple way to define a function that is the same as the F function, but only accepts 3 parameters.

def sum5 (A:int, B:int, C:int, D:int, e:int) = a + B + C + D +e//> SUM5: (A:int, B:int, C:int, D:int, E:int) Int val sum3 = SUM5 (_: int, 2, _: int, 3,_: int)//> sum3: (int, I NT, int) = = Int = <function3>

7. Special way to define and invoke a function (special function call forms)

Indefinite parameter, default value, named parameter equals python similar

8. Tail recursion

def approximate (guess:double): Double = if (Isgoodenough (guess)) Guess else approximate (improve (guess))

Note that the recursive call was the last

Thing that happens in the evaluation of function approximate ' s body. Functions like approximate, which call themselves as their last action, is called

tail recursive. The Scala compiler detects tail recursion and replaces it with

A jump back to the beginning of the function, after updating the function

Parameters with the new values.

So the tail recursion in Scala can achieve almost the same efficiency as the loop statement.

Programming in Scala (Second Edition) reading notes 6 functions and closures