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Write Android
like Scala
@petitviolet
Fringe81 Co,. Ltd.
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About me
• Hiroki Komurasaki
• @petitviolet
• Fringe81 Co., Ltd.
• Scala: Ad server
• Android (iOS): Ad SDK
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What is the pain
of Android?
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ON
NOT
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Nice point of Scala
• first class function
• `Awesome` data structures
• Option, List, Either, Future, Try, …
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Nice point of Scala
• first class function
• `Awesome` data structures
• Option, List, Either, Future, Try, …
• Functional Programming
• Monad
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Monad is
• `flatMap` in Scala
• `>>=` in Haskell
• “すごいH本”
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petitviolet/Android-Monad
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Maybe
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Maybe itemId = Maybe.of(x);
// Maybe findItemById(int id);
itemId.flatMap(this::findItemById)
.map(Item::getCost)
.map(integer -> integer + 5)
.filter(integer -> integer % 2 == 0)
.foreach(integer -> {
Log.d(TAG, "result: " + integer);
});
Maybe
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Maybe itemId = Maybe.of(x);
// Maybe findItemById(int id);
itemId.flatMap(this::findItemById)
.map(Item::getCost)
.map(integer -> integer + 5)
.filter(integer -> integer % 2 == 0)
.foreach(integer -> {
Log.d(TAG, "result: " + integer);
});
Maybe
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Maybe itemId = Maybe.of(x);
// Maybe findItemById(int id);
itemId.flatMap(this::findItemById)
.map(Item::getCost)
.map(integer -> integer + 5)
.filter(integer -> integer % 2 == 0)
.foreach(integer -> {
Log.d(TAG, "result: " + integer);
});
Maybe
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maybeInt.flatMap(new Function.F1>() {
@Override
public Maybe invoke(Integer integer) {
return findItemById(integer);
}
}).map(new Function.F1() {
@Override
public Integer invoke(Item item) {
return item.getCost();
}
}).map(new Function.F1() {
@Override
public Integer invoke(Integer integer) {
return integer + 5;
}
}).filter(new Function.F1() {
@Override
public Boolean invoke(Integer integer) {
return integer % 2 == 0;
}
}).foreach(new Function.F() {
@Override
public void invoke(Integer integer) {
Log.d(TAG, "result: " + integer);
}
});
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Maybe
• Null safe programming in Java
• if (foo != null)
• Maybe Monad
• of, flatMap
• Useful APIs
• map, getOrElse, foreach, filter, …
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ListM categoryIds = ListM.of(1, 2, 3);
ListM findItemsByCId(int id);
int sumCost = categoryIds
.flatMap(this::findItemsByCId)
.filter(item -> item.getStatus() == 1)
.map(Item::getCost)
.foldLeft(0, (acc, i) -> acc + i);
ListM
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ListM categoryIds = ListM.of(1, 2, 3);
ListM findItemsByCId(int id);
int sumCost = categoryIds
.flatMap(this::findItemsByCId)
.filter(item -> item.getStatus() == 1)
.map(Item::getCost)
.foldLeft(0, (acc, i) -> acc + i);
ListM
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ListM categoryIds = ListM.of(1, 2, 3);
ListM findItemsByCId(int id);
int sumCost = categoryIds
.flatMap(this::findItemsByCId)
.filter(item -> item.getStatus() == 1)
.map(Item::getCost)
.foldLeft(0, (acc, i) -> acc + i);
ListM
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ListM someViewListM = ListM.of(…);
int sumOfInput = someViewListM
.map(l -> ((EditText) l.findViewById(R.id.input)))
.map(editText -> editText.getText().toString())
.filterNot(s -> TextUtils.isEmpty(s))
.map(Integer::parseInt)
.foldLeft(0, (acc, i) -> acc + i);
ListM
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ListM someViewListM = ListM.of(…);
int sumOfInput = someViewListM
.map(l -> ((EditText) l.findViewById(R.id.input)))
.map(editText -> editText.getText().toString())
.filterNot(s -> TextUtils.isEmpty(s))
.map(Integer::parseInt)
.foldLeft(0, (acc, i) -> acc + i);
ListM
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ListM someViewListM = ListM.of(…);
int sumOfInput = someViewListM
.map(l -> ((EditText) l.findViewById(R.id.input)))
.map(editText -> editText.getText().toString())
.filterNot(s -> TextUtils.isEmpty(s))
.map(Integer::parseInt)
.foldLeft(0, (acc, i) -> acc + i);
ListM
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ListM
• List Monad
• of, unit, flatMap
• for(int i = 0; i <= list.size(); i++) { // }
• Useful Collection APIs
• map, foreach, filter, filterNot, partition
• foldLeft, foldRight, bindMaybe
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Android-Monad(0.5.0)
• Maybe
• ListM
• State
• Identity
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We are hiring!
fringe81.com/recruit