Recursive type
Discriminated unions can be recursive, that is they can refer to themselves in their definition. The prime example here is a tree:
type Tree =
| Branch of int * Tree list
| Leaf of int
As an example, let's define the following tree:
1
2 5
3 4
We can defi...
If you want to provide a URL out of convenience for your user but map it directly to another one you're already using. Use a redirect:
# config/routes.rb
TestApp::Application.routes.draw do
get 'courses/:course_name' => redirect('/courses/%{course_name}/lessons'), :as => "course"...
It is not possible to directly use static_cast, const_cast, dynamic_cast and reinterpret_cast on std::shared_ptr to retrieve a pointer sharing ownership with the pointer being passed as argument. Instead, the functions std::static_pointer_cast, std::const_pointer_cast, std::dynamic_pointer_cast and ...
Let's take a sample class.
class Book:
def __init__(self, title, author):
self.title = title
self.author = author
book1 = Book(title="Right Ho, Jeeves", author="P.G. Wodehouse")
In Python you can access the attribute title of the class using the dot ...
ChoiceDialog allows the user to pick one item from a list of options.
List<String> options = new ArrayList<>();
options.add("42");
options.add("9");
options.add("467829");
options.add("Other");
ChoiceDialog<String> dialog = new Choice...
For example, types for SI units have been standardized in the F# core library, in Microsoft.FSharp.Data.UnitSystems.SI. Open the appropriate sub-namespace, UnitNames or UnitSymbols, to use them. Or, if only a few SI units are required, they can be imported with type aliases:
/// Seconds, the SI uni...
Because generating documentation is based on markdown, you have to do 2 things :
1/ Write your doctest and make your doctest examples clear to improve readability (It is better to give a headline, like "examples" or "tests"). When you write your tests, do not forget to give 4 s...
Specifies how the database generates values for the property. There are three possible values:
None specifies that the values are not generated by the database.
Identity specifies that the column is an identity column, which is typically used for integer primary keys.
Computed specifies that th...
By Code-First convention, Entity Framework creates a column for every public property that is of a supported data type and has both a getter and a setter. [NotMapped] annotation must be applied to any properties that we do NOT want a column in a database table for.
An example of a property that we ...
Error handling is important but can make an elegant algorithm into a mess.
Railway Oriented Programming (ROP)
is used to make error handling elegant and composable.
Consider the simple function f:
let tryParse s =
let b, v = System.Int32.TryParse s
if b then Some v else None
let f (g : ...
UITextView has extra paddings by default. Sometimes it's annoying especially if you want to measure some text without view instance and place them at some area precisely.
Do this to remove such paddings.
messageTextView.textContainerInset = UIEdgeInsetsZero
messageTextView.textContainer.lineFragm...
Below query can be used to get TempDB database details:
USE [MASTER]
SELECT * FROM sys.databases WHERE database_id = 2
OR
USE [MASTER]
SELECT * FROM sys.master_files WHERE database_id = 2
With the help of below DMV, you can check how much TempDb space does your session is using. This query...
In VBA, Strings can be declared with a specific length; they are automatically padded or truncated to maintain that length as declared.
Public Sub TwoTypesOfStrings()
Dim FixedLengthString As String * 5 ' declares a string of 5 characters
Dim NormalString As String
Debug.Print Fi...
One of the most common obstacles using classes is finding the proper approach to handle private states.
There are 4 common solutions for handling private states:
Using Symbols
Symbols are new primitive type introduced on in ES2015,
as defined at MDN
A symbol is a unique and immutable data typ...
Dedicated Workers
A dedicated web worker is only accessible by the script that called it.
Main application:
var worker = new Worker('worker.js');
worker.addEventListener('message', function(msg) {
console.log('Result from the worker:', msg.data);
});
worker.postMessage([2,3]);
worker.j...
You can test for IndexedDB support in the current environment by checking for the presence of the window.indexedDB property:
if (window.indexedDB) {
// IndexedDB is available
}
Suppose we want to read and stack a bunch of similarly-formatted files. The quick solution is:
rbindlist(lapply(list.files(patt="csv$"), fread), id=TRUE)
We might not be satisfied with this for a couple reasons:
It might run into errors when reading with fread or when stacking with ...
Open Graph is a standard for metadata that extends the normal information contained within a site's head markup. This enables websites such as Facebook to display deeper and richer information about a website in a structured format. This information is then automatically displayed when users share l...
