Pro Android with Kotlin

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CHAPTER 10: Development
Multiline String Literals
Multiline string literals in Java always were a little clumsy to define.
String s = "First line\n" +
"Second line";
In Kotlin you can define multiline string literals as follows:
val s = """
First line
Second Line"""
You can even get rid of the preceding indent spaces by adding 
.trimIndent()
as follows:
val s = """
First line
Second Line""".trimIndent()
This removes the leading newline and the common spaces at the beginning of each line.
Inner Functions and Classes
In Kotlin, functions and classes can also be declared inside other functions, which further 
helps in structuring your code.
fun someFun() {
...
class InnerClass { ... }
fun innerFun() = ...
...
}
The scope of such inner constructs is of course limited to the function in which they are 
declared.
String Interpolation
In Kotlin you can pass values into strings as follows:
val i = 7
val s = "And the value of 'i' is ${i}"
This is borrowed from the Groovy language, and you can use it for all types since all types 
have a 
toString()
member. The only requirement is that the contents of 
${}
evaluate to an 
expression, so you can even write the following:
val i1 = 7
val i2 = 8
val s = "The sum is: ${i1+i2}"

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CHAPTER 10: Development
or write more complex constructs using method calls and lambda functions:
val s = "8 + 1 is: ${ { i: Int -> i + 1 }(8) }"
Qualified “this”
If 
this
is not what you want but you instead want to refer to 
this
from an outer context, in 
Kotlin you use the 
@
qualifier as follows:
class A {
val b = 7
init {
val p = arrayOf(8,9).apply {
this[0] += this@A.b
}
...
}
}
Delegation
Kotlin allows for easily following the delegation pattern. Here’s an example:
interface Printer {
fun print()
}
class PrinterImpl(val x: Int) : Printer {
override fun print() { print(x) }
}
class Derived(b: Printer) : Printer by b
Here, the class 
Derived
is of type 
Printer
and delegates all its method calls to the 
b
object. 
So, you can write the following:
val pi = PrinterImpl(7)
Derived(pi).print()
You are free to overwrite method calls at will, so you can adapt the delegate to use new 
functionalities.
class Derived(val b: Printer) : Printer by b {
override fun print() {
print("Printing:")
b.print()
}
}

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