Tutorial by Examples: d

if ([object respondsToSelector:@selector(someOptionalMethodInProtocol:)]) { [object someOptionalMethodInProtocol:argument]; }

Move Blue to the beginning of the array: NSMutableArray *myColors = [NSMutableArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil]; NSUInteger fromIndex = 2; NSUInteger toIndex = 0; id blue = [[[self.array objectAtIndex:fromIndex] retain]...

Every authenticated user has a Firebase uid that's unique across all providers and is returned in the result of every authentication method. A good way to store your user's data is to create a node to keep all the users's data and to protect it using your security rules - Database { "use...

The dynamic keyword is used with dynamically typed objects. Objects declared as dynamic forego compile-time static checks, and are instead evaluated at runtime. using System; using System.Dynamic; dynamic info = new ExpandoObject(); info.Id = 123; info.Another = 456; Console.WriteLine(info...

Evaluates to the second argument if and only if both of the arguments are truthy. Otherwise evaluates to the first falsey argument. x = True y = True z = x and y # z = True x = True y = False z = x and y # z = False x = False y = True z = x and y # z = False x = False y = False z =...

Deleting files The unlink function deletes a single file and returns whether the operation was successful. $filename = '/path/to/file.txt'; if (file_exists($filename)) { $success = unlink($filename); if (!$success) { throw new Exception("Cannot delete $filename&qu...

This example will guide you through setting up a back end serving an a Hello World HTML page. Installing Requirements Order matters for this step! sudo apt-get install apache2 Setting up the HTML Apache files live in /var/www/html/. Lets quickly get there. Make sure you're in your root ...

for typescript 2.x: definitions from DefinitelyTyped are available via @types npm package npm i --save lodash npm i --save-dev @types/lodash but in case if you want use types from other repos then can be used old way: for typescript 1.x: Typings is an npm package that can automatically insta...

This function lets you iterate over the Cartesian product of a list of iterables. For example, for x, y in itertools.product(xrange(10), xrange(10)): print x, y is equivalent to for x in xrange(10): for y in xrange(10): print x, y Like all python functions that accept a v...

Any data structure that supports __getitem__ can have their nested structure formatted: person = {'first': 'Arthur', 'last': 'Dent'} '{p[first]} {p[last]}'.format(p=person) # 'Arthur Dent' Object attributes can be accessed using getattr(): class Person(object): first = 'Zaphod' la...

Lambda functions in C++ are syntactic sugar that provide a very concise syntax for writing functors. As such, equivalent functionality can be obtained in C++03 (albeit much more verbose) by converting the lambda function into a functor: // Some dummy types: struct T1 {int dummy;}; struct T2 {int ...

There are a couple of ways to delete a column in a DataFrame. import numpy as np import pandas as pd np.random.seed(0) pd.DataFrame(np.random.randn(5, 6), columns=list('ABCDEF')) print(df) # Output: # A B C D E F # 0 -0.895467 0.386902...

This example assumes you know how to test a Flask app using pytest Below is an API that takes a JSON input with integer values a and b e.g. {"a": 1, "b": 2}, adds them up and returns sum a + b in a JSON response e.g. {"sum": 3}. # hello_add.py from flask import Flask...

Broadcast variables are read only shared objects which can be created with SparkContext.broadcast method: val broadcastVariable = sc.broadcast(Array(1, 2, 3)) and read using value method: val someRDD = sc.parallelize(Array(1, 2, 3, 4)) someRDD.map( i => broadcastVariable.value.apply(...

fs.access() determines whether a path exists and what permissions a user has to the file or directory at that path. fs.access doesn't return a result rather, if it doesn't return an error, the path exists and the user has the desired permissions. The permission modes are available as a property on ...

Due to Node's asynchronous nature, creating or using a directory by first: checking for its existence with fs.stat(), then creating or using it depending of the results of the existence check, can lead to a race condition if the folder is created between the time of the check and the time of ...

The nodemon package makes it possible to automatically reload your program when you modify any file in the source code. Installing nodemon globally npm install -g nodemon (or npm i -g nodemon) Installing nodemon locally In case you don't want to install it globally npm install --save-dev nodemo...

Once Pandas has been installed, you can check if it is is working properly by creating a dataset of randomly distributed values and plotting its histogram. import pandas as pd # This is always assumed but is included here as an introduction. import numpy as np import matplotlib.pyplot as plt ...

In $e:expr, the expr is called the fragment specifier. It tells the parser what kind of tokens the parameter $e is expecting. Rust provides a variety of fragment specifiers to, allowing the input to be very flexible. SpecifierDescriptionExamplesidentIdentifierx, foopathQualified namestd::collection...

Exporting a macro to allow other modules to use it: #[macro_export] // ^~~~~~~~~~~~~~~ Think of it as `pub` for macros. macro_rules! my_macro { (..) => {..} } Using macros from other crates or modules: #[macro_use] extern crate lazy_static; // ^~~~~~~~~~~~ Must add this in ord...