info/learnxinyminutes-docs
1
0
Fork 0
mirror of https://github.com/adambard/learnxinyminutes-docs.git synced 2025-08-07 23:37:32 +02:00
Code Issues Releases Wiki Activity

Merge pull request #857 from geoffliu/master

Browse Source 
[Scala/en] Reorganize the Scala tutorial
This commit is contained in:
Adam Bard
2014-11-12 19:52:39 +02:00
parent ad951f2615 29bc9a1449
commit 493cff577c
1 changed files with 219 additions and 178 deletions
Download Patch File Download Diff File Expand all files Collapse all files

397
scala.html.markdown
View File

@@ -4,6 +4,7 @@ filename: learnscala.scala
contributors: contributors:
- ["George Petrov", "http://github.com/petrovg"] - ["George Petrov", "http://github.com/petrovg"]
- ["Dominic Bou-Samra", "http://dbousamra.github.com"] - ["Dominic Bou-Samra", "http://dbousamra.github.com"]
- ["Geoff Liu", "http://geoffliu.me"]
filename: learn.scala filename: learn.scala
--- ---
@@ -20,34 +21,47 @@ Scala - the scalable language
scala> scala>
This is the so called REPL. You can run commands in the REPL. Let's do just This is the so called REPL (Read-Eval-Print Loop). You may type any valid
that: Scala expression into it, and the result will be printed. We will explain what
Scala files look like further into this tutorial, but for now, let's start
with some basics.
*/ */
println(10) // prints the integer 10
println("Boo!") // printlns the string Boo! /////////////////////////////////////////////////
// 1. Basics
/////////////////////////////////////////////////
// Single line comments start with two forward slashes
// Some basics /*
Multi line comments, as you can already see from above, look like this.
*/
// Printing, and forcing a new line on the next print // Printing, and forcing a new line on the next print
println("Hello world!") println("Hello world!")
println(10)
// Printing, without forcing a new line on next print // Printing, without forcing a new line on next print
print("Hello world") print("Hello world")
// Declaring values is done using either var or val // Declaring values is done using either var or val.
// val declarations are immutable, whereas var's are mutable. Immutability is // val declarations are immutable, whereas var's are mutable. Immutability is
// a good thing. // a good thing.
val x = 10 // x is now 10 val x = 10 // x is now 10
x = 20 // error: reassignment to val x = 20 // error: reassignment to val
var x = 10 var y = 10
x = 20 // x is now 20 y = 20 // y is now 20
// Single line comments start with two forward slashes /*
/* Scala is a statically typed language, yet note that in the above declarations, we did not specify
Multi line comments look like this. a type. This is due to a language feature called type inference. In most cases, Scala compiler can
guess what the type of a variable is, so you don't have to type it every time. We can explicitly
declare the type of a variable like so:
*/ */
val z: Int = 10
val a: Double = 1.0
val b: Double = 10 // Notice automatic conversion from Int to Double, result is 10.0, not 10
// Boolean values // Boolean values
true true
@@ -64,9 +78,11 @@ true == false // false
2 - 1 // 1 2 - 1 // 1
5 * 3 // 15 5 * 3 // 15
6 / 2 // 3 6 / 2 // 3
6 / 4 // 1
6.0 / 4 // 1.5
// Evaluating a command in the REPL gives you the type and value of the result // Evaluating an expression in the REPL gives you the type and value of the result
1 + 7 1 + 7
@@ -78,23 +94,63 @@ true == false // false
This means the result of evaluating 1 + 7 is an object of type Int with a This means the result of evaluating 1 + 7 is an object of type Int with a
value of 8 value of 8
1+7 will give you the same result Note that "res29" is a sequentially generated variable name to store the results of the
expressions you typed, your output may differ.
*/ */
"Scala strings are surrounded by double quotes"
'a' // A Scala Char
// 'Single quote strings don't exist' <= This causes an error
// Everything is an object, including a function. Type these in the REPL: // Strings have the usual Java methods defined on them
"hello world".length
"hello world".substring(2, 6)
"hello world".replace("C", "3")
7 // results in res30: Int = 7 (res30 is just a generated var name for the result) // They also have some extra Scala methods. See also: scala.collection.immutable.StringOps
"hello world".take(5)
"hello world".drop(5)
// String interpolation: notice the prefix "s"
val n = 45
s"We have $n apples" // => "We have 45 apples"
// Expressions inside interpolated strings are also possible
val a = Array(11, 9, 6)
s"My second daughter is ${a(0) - a(2)} years old." // => "My second daughter is 5 years old."
s"We have double the amount of ${n / 2.0} in apples." // => "We have double the amount of 22.5 in apples."
s"Power of 2: ${math.pow(2, 2)}" // => "Power of 2: 4"
// Formatting with interpolated strings with the prefix "f"
f"Power of 5: ${math.pow(5, 2)}%1.0f" // "Power of 5: 25"
f"Square root of 122: ${math.sqrt(122)}%1.4f" // "Square root of 122: 11.0454"
// Raw strings, ignoring special characters.
raw"New line feed: \n. Carriage return: \r." // => "New line feed: \n. Carriage return: \r."
// Some characters need to be "escaped", e.g. a double quote inside a string:
"They stood outside the \"Rose and Crown\"" // => "They stood outside the "Rose and Crown""
// Triple double-quotes let strings span multiple rows and contain quotes
val html = """<form id="daform">
<p>Press belo', Joe</p>
<input type="submit">
</form>"""
/////////////////////////////////////////////////
// 2. Functions
/////////////////////////////////////////////////
// The next line gives you a function that takes an Int and returns it squared // The next line gives you a function that takes an Int and returns it squared
(x:Int) => x * x (x:Int) => x * x
// You can assign this function to an identifier, like this: // You can assign this function to an identifier, like this:
val sq = (x:Int) => x * x val sq = (x:Int) => x * x
/* The above says this /* The above says this
sq: Int => Int = <function1> sq: Int => Int = <function1>
Which means that this time we gave an explicit name to the value - sq is a Which means that this time we gave an explicit name to the value - sq is a
function that take an Int and returns Int. function that take an Int and returns Int.
@@ -105,28 +161,68 @@ val sq = (x:Int) => x * x
sq(10) // Gives you this: res33: Int = 100. sq(10) // Gives you this: res33: Int = 100.
// The colon explicitly defines the type of a value, in this case a function // The colon explicitly defines the type of a value, in this case a function
// taking an Int and returning an Int. // taking an Int and returning an Int.
val add10: Int => Int = _ + 10 val add10: Int => Int = _ + 10
// Scala allows methods and functions to return, or take as parameters, other
// functions or methods.
List(1, 2, 3) map add10 // List(11, 12, 13) - add10 is applied to each element
// Anonymous functions can be used instead of named functions:
List(1, 2, 3) map (x => x + 10)
// And the underscore symbol, can be used if there is just one argument to the
// anonymous function. It gets bound as the variable
List(1, 2, 3) map (_ + 10)
// If the anonymous block AND the function you are applying both take one
// argument, you can even omit the underscore
List("Dom", "Bob", "Natalia") foreach println
/////////////////////////////////////////////////
// 3. Flow Control
/////////////////////////////////////////////////
// Data structures 1 to 5
val r = 1 to 5
r.foreach( println )
r foreach println
// NB: Scala is quite lenient when it comes to dots and brackets - study the
// rules separately. This helps write DSLs and APIs that read like English
(5 to 1 by -1) foreach ( println )
// A while loops
var i = 0
while (i < 10) { println("i " + i); i+=1 }
while (i < 10) { println("i " + i); i+=1 } // Yes, again. What happened? Why?
i // Show the value of i. Note that while is a loop in the classical sense -
// it executes sequentially while changing the loop variable. while is very
// fast, faster that Java // loops, but using the combinators and
// comprehensions above is easier to understand and parallelize
// A do while loop
do {
println("x is still less than 10");
x += 1
} while (x < 10)
// Tail recursion is an idiomatic way of doing recurring things in Scala.
// Recursive functions need an explicit return type, the compiler can't infer it.
// Here it's Unit.
def showNumbersInRange(a:Int, b:Int):Unit = {
print(a)
if (a < b)
showNumbersInRange(a + 1, b)
}
showNumbersInRange(1,14)
// Conditionals
val x = 10
if (x == 1) println("yeah")
if (x == 10) println("yeah")
if (x == 11) println("yeah")
if (x == 11) println ("yeah") else println("nay")
println(if (x == 10) "yeah" else "nope")
val text = if (x == 10) "yeah" else "nope"
/////////////////////////////////////////////////
// 4. Data Structures
/////////////////////////////////////////////////
val a = Array(1, 2, 3, 5, 8, 13) val a = Array(1, 2, 3, 5, 8, 13)
a(0) a(0)
@@ -145,8 +241,8 @@ val s = Set(1, 3, 7)
s(0) s(0)
s(1) s(1)
/* Look up the documentation of map here - /* Look up the documentation of map here -
* http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Map * http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Map
* and make sure you can read it * and make sure you can read it
*/ */
@@ -175,110 +271,25 @@ d._1
d._2 d._2
/////////////////////////////////////////////////
// 5. Object Oriented Programming
/////////////////////////////////////////////////
// Combinators /*
Aside: Everything we've done so far in this tutorial has been simple
expressions (values, functions, etc). These expressions are fine to type into
the command-line interpreter for quick tests, but they cannot exist by
themselves in a Scala file. For example, you cannot have just "val x = 5" in
a Scala file. Instead, the only top-level constructs allowed in Scala are:
s.map(sq) - objects
- classes
- case classes
- traits
val sSquared = s. map(sq) And now we will explain what these are.
*/
sSquared.filter(_ < 10)
sSquared.reduce (_+_)
// The filter function takes a predicate (a function from A -> Boolean) and
// selects all elements which satisfy the predicate
List(1, 2, 3) filter (_ > 2) // List(3)
case class Person(name: String, age: Int)
List(
Person(name = "Dom", age = 23),
Person(name = "Bob", age = 30)
).filter(_.age > 25) // List(Person("Bob", 30))
// Scala a foreach method defined on certain collections that takes a type
// returning Unit (a void method)
val aListOfNumbers = Set(1,2,3,45,234)
aListOfNumbers foreach (x => println(x))
aListOfNumbers foreach println
// For comprehensions
for { n <- s } yield sq(n)
val nSquared2 = for { n <- s } yield sq(n)
for { n <- nSquared2 if n < 10 } yield n
for { n <- s; nSquared = n * n if nSquared < 10} yield nSquared
/* NB Those were not for loops. The semantics of a for loop is 'repeat', whereas
a for-comprehension defines a relationship between two sets of data. */
// Loops and iteration
1 to 5
val r = 1 to 5
r.foreach( println )
r foreach println
// NB: Scala is quite lenient when it comes to dots and brackets - study the
// rules separately. This helps write DSLs and APIs that read like English
(5 to 1 by -1) foreach ( println )
// A while loops
var i = 0
while (i < 10) { println("i " + i); i+=1 }
while (i < 10) { println("i " + i); i+=1 } // Yes, again. What happened? Why?
i // Show the value of i. Note that while is a loop in the classical sense -
// it executes sequentially while changing the loop variable. while is very
// fast, faster that Java // loops, but using the combinators and
// comprehensions above is easier to understand and parallelize
// A do while loop
do {
println("x is still less than 10");
x += 1
} while (x < 10)
// Tail recursion is an idiomatic way of doing recurring things in Scala.
// Recursive functions need an explicit return type, the compiler can't infer it.
// Here it's Unit.
def showNumbersInRange(a:Int, b:Int):Unit = {
print(a)
if (a < b)
showNumbersInRange(a + 1, b)
}
showNumbersInRange(1,14)
// Conditionals
val x = 10
if (x == 1) println("yeah")
if (x == 10) println("yeah")
if (x == 11) println("yeah")
if (x == 11) println ("yeah") else println("nay")
println(if (x == 10) "yeah" else "nope")
val text = if (x == 10) "yeah" else "nope"
// Object oriented features
// Classname is Dog
class Dog(br: String) { class Dog(br: String) {
var breed: String = br var breed: String = br
//A method called bark, returning a String //A method called bark, returning a String
@@ -296,8 +307,6 @@ println(mydog.bark) // => "Woof, woof!"
// Classes can contain nearly any other construct, including other classes, // Classes can contain nearly any other construct, including other classes,
// functions, methods, objects, case classes, traits etc. // functions, methods, objects, case classes, traits etc.
// Case classes // Case classes
case class Person(name:String, phoneNumber:String) case class Person(name:String, phoneNumber:String)
@@ -305,8 +314,12 @@ case class Person(name:String, phoneNumber:String)
Person("George", "1234") == Person("Kate", "1236") Person("George", "1234") == Person("Kate", "1236")
// Objects and traits coming soon!
// Pattern matching
/////////////////////////////////////////////////
// 6. Pattern Matching
/////////////////////////////////////////////////
val me = Person("George", "1234") val me = Person("George", "1234")
@@ -345,49 +358,77 @@ matcher("52917") // => "No match on '52917'"
matcher("52752-16432-22178-47917") // => "Serial key: 52752, 16432, 22178, 47917" matcher("52752-16432-22178-47917") // => "Serial key: 52752, 16432, 22178, 47917"
// Strings /////////////////////////////////////////////////
// 7. Functional Programming
/////////////////////////////////////////////////
"Scala strings are surrounded by double quotes" // // Scala allows methods and functions to return, or take as parameters, other
'a' // A Scala Char // functions or methods.
'Single quote strings don't exist' // Error
"Strings have the usual Java methods defined on them".length
"They also have some extra Scala methods.".reverse
// Seealso: scala.collection.immutable.StringOps List(1, 2, 3) map add10 // List(11, 12, 13) - add10 is applied to each element
println("ABCDEF".length) // Anonymous functions can be used instead of named functions:
println("ABCDEF".substring(2, 6)) List(1, 2, 3) map (x => x + 10)
println("ABCDEF".replace("C", "3"))
// String interpolation // And the underscore symbol, can be used if there is just one argument to the
val n = 45 // anonymous function. It gets bound as the variable
println(s"We have $n apples") // => "We have 45 apples" List(1, 2, 3) map (_ + 10)
// Expressions inside interpolated strings are also possible // If the anonymous block AND the function you are applying both take one
val a = Array(11, 9, 6) // argument, you can even omit the underscore
println(s"My second daughter is ${a(0) - a(2)} years old.") // => "My second daughter is 5 years old." List("Dom", "Bob", "Natalia") foreach println
println(s"We have double the amount of ${n / 2.0} in apples.") // => "We have double the amount of 22.5 in apples."
println(s"Power of 2: ${math.pow(2, 2)}") // => "Power of 2: 4"
// Formatting with interpolated strings (note the prefixed f)
println(f"Power of 5: ${math.pow(5, 2)}%1.0f") // "Power of 5: 25"
println(f"Square root of 122: ${math.sqrt(122)}%1.4f") // "Square root of 122"
// Ignoring special characters.
println(raw"New line feed: \n. Carriage return: \r.") // => "New line feed: \n. Carriage return: \r."
// Some characters need to be 'escaped', e.g. a double quote inside a string:
val a = "They stood outside the \"Rose and Crown\"" // => "They stood outside the "Rose and Crown""
// Triple double-quotes let strings span multiple rows and contain quotes
val html = """<form id="daform">
<p>Press belo', Joe</p>
| <input type="submit">
</form>"""
// Combinators
// Application structure and organization s.map(sq)
val sSquared = s. map(sq)
sSquared.filter(_ < 10)
sSquared.reduce (_+_)
// The filter function takes a predicate (a function from A -> Boolean) and
// selects all elements which satisfy the predicate
List(1, 2, 3) filter (_ > 2) // List(3)
case class Person(name:String, phoneNumber:String)
List(
Person(name = "Dom", age = 23),
Person(name = "Bob", age = 30)
).filter(_.age > 25) // List(Person("Bob", 30))
// Scala a foreach method defined on certain collections that takes a type
// returning Unit (a void method)
val aListOfNumbers = List(1, 2, 3, 4, 10, 20, 100)
aListOfNumbers foreach (x => println(x))
aListOfNumbers foreach println
// For comprehensions
for { n <- s } yield sq(n)
val nSquared2 = for { n <- s } yield sq(n)
for { n <- nSquared2 if n < 10 } yield n
for { n <- s; nSquared = n * n if nSquared < 10} yield nSquared
/* NB Those were not for loops. The semantics of a for loop is 'repeat', whereas
a for-comprehension defines a relationship between two sets of data. */
/////////////////////////////////////////////////
// 8. Implicits
/////////////////////////////////////////////////
Coming soon!
/////////////////////////////////////////////////
// 9. Misc
/////////////////////////////////////////////////
// Importing things // Importing things
import scala.collection.immutable.List import scala.collection.immutable.List