Tutorial by Examples: ga

Pattern matching allows to deconstruct complex values and it is by no way limited to the “outer most” level of the representation of a value. To illustrate this, we implement the function transforming a boolean expression into a boolean expression where all negations are only on atoms, the so calle...

The List.fold_left and List.fold_right functions are higher-order functions that implement the outer logic of list aggregation. Aggregating a list, sometimes also referred to as reducing a list, means computing a value derived from the sequential inspection of all items in that list. The documenta...

In Elm, reducing functions are called "folds", and there are two standard methods to "fold" values up: from the left, foldl, and from the right, foldr. > List.foldl (+) 0 [1,2,3] 6 : number The arguments to foldl and foldr are: reducing function: newValue -> accumul...

A reference to an option &Option<T> cannot be unwrapped if the type T is not copyable. The solution is to change the option to &Option<&T> using as_ref(). Rust forbids transferring of ownership of objects while the objects are borrowed. When the Option itself is borrowed (&a...

The C++ approach - new and delete In a language like C++, the application program is responsible for managing the memory used by dynamically allocated memory. When an object is created in the C++ heap using the new operator, there needs to be a corresponding use of the delete operator to dispose o...

A simple example on how to read a UTF text file synchronously. import flash.filesystem.File; import flash.filesystem.FileMode; import flash.filesystem.FileStream; //First, get a reference to the file you want to load var myFile:File = File.documentsDirectory.resolvePath("lifestory.txt&...

This example uses a search controller to filter the data inside a table view controller. The search bar is placed inside the navigation bar that the table view is embedded into. Embed a UITableViewController into a UINavigationController to get the UINavigationItem (which contains the navigation ...

This program illustrates how one can copy a file using readable and writable streams using the createReadStream(), and createWriteStream() functions provided by the file system module. //Require the file System module var fs = require('fs'); /* Create readable stream to file in current direc...

Sometimes it might be necessary to manually promisify a callback function. This could be for a case where the callback does not follow the standard error-first format or if additional logic is needed to promisify: Example with fs.exists(path, callback): var fs = require('fs'); var existsAsync =...

Screen shot: Option 1 (pure adb) The shell adb command allows us to execute commands using a device's built-in shell. The screencap shell command captures the content currently visible on a device and saves it into a given image file, e.g. /sdcard/screen.png: adb shell screencap /sdcard/screen.png...

Provided an App.GoogleMap coffee script class, the google map can be initialized like this: # app/assets/javascripts/google_maps.js.coffee # ... class App.GoogleMap map_div: {} map: {} constructor: (map_div)-> @map_div = map_div @init_map() @reference_the_map_as_dat...

Provided an App.GoogleMap coffee script class and the marker information being stored in the data-address-fields attribute of the .google_map div, the map markers can be initialized on the map like this: # app/assets/javascripts/google_maps.js.coffee # ... class App.GoogleMap # ... markers:...

Provided an App.GoogleMap coffee script class with the google.maps.Map stored as @map and the google.maps.Markers stored as @markers, the map can be auto-zoomed, i.e. adjusted that all markers are visible, like this: on the map like this: # app/assets/javascripts/google_maps.js.coffee # ... cla...

An easy way to clone an object is by implementing a copy constructor. public class Sheep { private String name; private int weight; public Sheep(String name, int weight) { this.name = name; this.weight = weight; } // copy constructor // copies...

To generate a new mailer, enter the following command rails generate mailer PostMailer This will generate a blank template file in app/mailers/post_mailer.rb named PostMailer class PostMailer < ApplicationMailer end Two layout files will also be generated for the email view, one for the...

Rails provides a lot of generators, for controllers too of course. You can generate a new controller by running this command in your app folder rails generate controller NAME [action action] [options] Note: You can also use rails g alias to invoke rails generate For example, to generate a cont...

You can rescue a RecordNotFound exception with a redirect instead of showing an error page: class ApplicationController < ActionController::Base # your other stuff rescue_from ActiveRecord::RecordNotFound do |exception| redirect_to root_path, 404, alert: I18n.t("errors.record...

Debug.log's second argument is always returned, so you could write code like the following and it would just work: update : Msg -> Model -> (Model, Cmd Msg) update msg model = case Debug.log "The Message" msg of Something -> ... Replacing case msg o...

The following example can be tested on https://ellie-app.com/m9tk39VpQg/0. import Html exposing (..) import Json.Decode payload = """ ["fu", "bar"] """ main = Json.Decode.decodeString decoder payload -- Ok ["fu","b...

First it is important to understand that the Core Data Model is the *.xcdatamodeld file. You will notice you have not entities. You will have to create one yourself. At the bottom of Xcode you will notice a button that says "Add Entity" click it and you will have a new entity in the ...