A common use case for extension methods is to improve an existing API. Here are examples of adding exist, notExists and deleteRecursively to the Java 7+ Path class:
fun Path.exists(): Boolean = Files.exists(this)
fun Path.notExists(): Boolean = !this.exists()
fun Path.deleteRecursively(): Bool...
In Kotlin you could write code like:
val x: Path = Paths.get("dirName").apply {
if (Files.notExists(this)) throw IllegalStateException("The important file does not exist")
}
But the use of apply is not that clear as to your intent. Sometimes it is clearer to create a ...
With this declaration:
fun Temporal.toIsoString(): String = DateTimeFormatter.ISO_INSTANT.format(this)
You can now simply:
val dateAsString = someInstant.toIsoString()
If you want to extend a class as-if you are a static function, for example for class Something add static looking function fromString, this can only work if the class has a companion object and that the extension function has been declared upon the companion object:
class Something {
compani...
Kotlin allows us to provide implementations for a predefined set of operators with fixed symbolic representation (like + or *) and fixed precedence. To implement an operator, we provide a member function or an extension function with a fixed name, for the corresponding type. Functions that overload ...
For instance, two tables are given,
T1
id x y
8 42 1.9
9 30 1.9
T2
id signal
8 55
8 56
8 59
9 57
9 58
9 60
The goal is to get the new table T3:
id x y s1 s2 s3
8 42 1.9 55 ...
To get Unix Epoch Time, use the constant timeIntervalSince1970:
Swift
let date = NSDate() // current date
let unixtime = date.timeIntervalSince1970
Objective-C
NSDate *date = [NSDate date]; // current date
int unixtime = [date timeIntervalSince1970];
Uppercase and lowercase letters of the alphabet are equivalent in the
Fortran character set. In other words, Fortran is case insensitive. This behavior is in contrast with case-sensitive languages, such as C++ and many others.
As a consequence, the variables a and A are the same variable. In princ...
Let's say we want to replace only numbers with 2 digits: regular expression will find them with (\d\d)
SELECT REGEXP_REPLACE ('2, 5, and 10 are numbers in this example', '(\d\d)', '#')
FROM dual;
Results in:
'2, 5, and # are numbers in this example'
If I want to swap parts of the text, I us...
Let's say you have an object like this:
var myObject = {
name: 'Peter'
}
Later in your code, you try to access myObject.name and you get George instead of Peter. You start wondering who changed it and where exactly it was changed. There is a way to place a debugger (or something else) on e...
Use Nested Loops.
Usage : use_nl(A B)
This hint will ask the engine to use nested loop method to join the tables A and B. That is row by row comparison. The hint does not force the order of the join, just asks for NL.
SELECT /*+use_nl(e d)*/ *
FROM Employees E
JOIN Departments D on E.Department...
"Use DIRECT PATH method for inserting new rows".
The APPEND hint instructs the engine to use direct path load. This means that the engine will not use a conventional insert using memory structures and standard locks, but will write directly to the tablespace the data. Always creates new b...
In the simple example, we simply set the width of the rectangle to that of it's parent. Let's consider a more complicated example:
ApplicationWindow {
visible: true
width: 400
height: 640
Rectangle{
id: rect
anchors.centerIn: parent
height: 100
...
Sample Data:
CREATE TABLE table_name ( id, list ) AS
SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list
SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list
SELECT 3, NULL FROM DUAL UNION ALL -- NULL list
SELECT 4, 'f,,g' FROM DUAL; -- NULL item...
Sample Data:
CREATE TABLE table_name ( id, list ) AS
SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list
SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list
SELECT 3, NULL FROM DUAL UNION ALL -- NULL list
SELECT 4, 'f,,g' FROM DUAL; -- NULL item...
Sample Data:
CREATE TABLE table_name ( id, list ) AS
SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list
SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list
SELECT 3, NULL FROM DUAL UNION ALL -- NULL list
SELECT 4, 'f,,g' FROM DUAL; -- NULL item...
