Tutorial by Examples: i

interface ITable { // an indexer can be declared in an interface object this[int x, int y] { get; set; } } class DataTable : ITable { private object[,] cells = new object[10, 10]; /// <summary> /// implementation of the indexer declared in the interface //...

4.0 Declare an associative array declare -A aa Declaring an associative array before initialization or use is mandatory. Initialize elements You can initialize elements one at a time as follows: aa[hello]=world aa[ab]=cd aa["key with space"]="hello world" You can al...

Get the list of inialized indexes in an array $ arr[2]='second' $ arr[10]='tenth' $ arr[25]='twenty five' $ echo ${!arr[@]} 2 10 25

sqldf() from the package sqldf allows the use of SQLite queries to select and manipulate data in R. SQL queries are entered as character strings. To select the first 10 rows of the "diamonds" dataset from the package ggplot2, for example: data("diamonds") head(diamonds) #...

Windows There are two options how to install Kivy: First ensure python tools are up-to-date. python -m pip install --upgrade pip wheel setuptools Then install the basic dependencies. python -m pip install docutils pygments pypiwin32 kivy.deps.sdl2 kivy.deps.glew Although Kivy already has p...

The JsonPipe can be used for debugging the state of any given internal. Code @Component({ selector: 'json-example', template: `<div> <p>Without JSON pipe:</p> <pre>{{object}}</pre> <p>With JSON pipe:</p> <pre>{{object | json...

You can install three.js via npm: npm install three You can add it from a CDN to your HTML: <script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r83/three.js"></script> You can use the three.js editor to give it a try and download the project as an ex...

Arithmetic if statement allows one to use three branches depending on the result of an arithmetic expression if (arith_expr) label1, label2, label3 This if statement transfers control flow to one of the labels in a code. If the result of arith_expr is negative label1 is involved, if the result i...

Detailed instructions on getting tfs set up or installed.

This validation restricts the insertion of only numeric values. class Player < ApplicationRecord validates :points, numericality: true validates :games_played, numericality: { only_integer: true } end Besides :only_integer, this helper also accepts the following options to add constrai...

This helper validates that the attribute's value is unique right before the object gets saved. class Account < ApplicationRecord validates :email, uniqueness: true end There is a :scope option that you can use to specify one or more attributes that are used to limit the uniqueness check: ...

This helper validates that the specified attributes are not empty. class Person < ApplicationRecord validates :name, presence: true end Person.create(name: "John").valid? # => true Person.create(name: nil).valid? # => false You can use the absence helper to validate th...

Use following methods if you want to skip the validations. These methods will save the object to the database even if it is invalid. decrement! decrement_counter increment! increment_counter toggle! touch update_all update_attribute update_column update_columns update_counters You ca...

class Person < ApplicationRecord validates :name, length: { minimum: 2 } validates :bio, length: { maximum: 500 } validates :password, length: { in: 6..20 } validates :registration_number, length: { is: 6 } end The possible length constraint options are: :minimum - The attribut...

The special attribute __name__ of a function, class or module is a string containing its name. import os class C: pass def f(x): x += 2 return x print(f) # <function f at 0x029976B0> print(f.__name__) # f print(C) # <class '__main__.C'> print(C.__name__...

Unlike Big-O notation, which represents only upper bound of the running time for some algorithm, Big-Theta is a tight bound; both upper and lower bound. Tight bound is more precise, but also more difficult to compute. The Big-Theta notation is symmetric: f(x) = Ө(g(x)) <=> g(x) = Ө(f(x)) An ...

Overload resolution occurs after name lookup. This means that a better-matching function will not be selected by overload resolution if it loses name lookup: void f(int x); struct S { void f(double x); void g() { f(42); } // calls S::f because global f is not visible here, ...

While it might seem counterintuitive, you can use logical operators to determine whether or not a statement is run. For instance: File.exist?(filename) or STDERR.puts "#{filename} does not exist!" This will check to see if the file exists and only print the error message if it doesn't....

You can create parser error messages according to your script needs. This is through the argparse.ArgumentParser.error function. The below example shows the script printing a usage and an error message to stderr when --foo is given but not --bar. import argparse parser = argparse.ArgumentParser...

First: The path structure If you don't have it you need to create the middleware folder within your app following the structure: yourproject/yourapp/middleware The folder middleware should be placed in the same folder as settings.py, urls, templates... Important: Don't forget to create the ini...