July 2016
Beginner to intermediate
776 pages
17h 26m
Korean
Content preview from 프로그래밍 스칼라: 실용적인 스칼라 활용법을 익히는 가장 확실한 실전 바이블 (2.11.x 버전 기반)
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574
3
부
기초를 넘어서
implicit val optionReduce
=
new Reduce1
[
Option
]
{
def reduce
[
T
](
opt
:
Option
[
T
])(
f
:
(
T
,
T
)
=
>
T
):
T
=
opt reduce f
}
}
➊
Reduce1
추상화에는 타입 매개변수가
M
하나밖에 없다. 고계타입
M
은 여전히 반공변적이지
만, 그 안의 타입 매개변수는 여기서 지정하지 않았다. 따라서 이는 존재 타입이 된다(
14
.
9
절
‘존재 타입’을 보라 ). 대신
T
매개변수를
reduce
메서드 쪽으로 옮겼다.
➋ 암시인
seqReduce
와
optionReduce
를 이제는 메서드가 아닌 값으로 정의한다.
앞에서는 타입 매개변수
T
를 추론할 수 있도록 암시적 메서드를 사용했지만, 이제는 실제
reduce
를 호출하기 전까지 타입 추론을 유예시킬 수 있도록 타입 인스턴스가 하나만 존재한다.
변경한
sum
메서드는 더 간단하며, 결과도 동일하다 (결과는 따로 표시하지 않음).
//
src
/
main
/
scala
/
progscala2
/
typesystem
/
higherkinded
/
add1
.
sc
...
def sum
[
T
:
Add
,
M
[
_
]
:
Reduce1
](
container
:
M
[
T
]):
T
=
implicitly
[
Reduce1
[
M
]].
reduce
(
container
)(
implicitly ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.