Tutorial by Examples: u

C# developers get a lot of null reference exceptions to deal with. F# developers don't because they have the Option type. An Option<> type (some prefer Maybe<> as a name) provides a Some and a None return type. It makes it explicit that a method may be about to return a null record. For...

enum Util { /* No instances */; public static int clamp(int min, int max, int i) { return Math.min(Math.max(i, min), max); } // other utility methods... } Just as enum can be used for singletons (1 instance classes), it can be used for utility classes (0 instance...

Imagine that we have a class Math.php with logic of calculating of fiobanacci and factorial numbers. Something like this: <?php class Math { public function fibonacci($n) { if (is_int($n) && $n > 0) { $elements = array(); $elements[1] = 1; ...

install the required Microsoft.SqlServer.Types assembly; they are not installed by default, and are available from Microsoft here as "Microsoft® System CLR Types for Microsoft® SQL Server® 2012" - note that there are separate installers for x86 and x64. install Dapper.EntityFramew...

Once the type handlers are registered, everything should work automatically, and you should be able to use these types as either parameters or return values: string redmond = "POINT (122.1215 47.6740)"; DbGeography point = DbGeography.PointFromText(redmond, DbGeography.DefaultCoordi...

When using Access you can retrieve data using queries. These queries are built using Structured Query Language (SQL). Understanding SQL is important because it can help build better, more useful queries. When creating queries in Access, you can switch to "SQL View". An example of a "...

When you wish to combine the results of multiple tables or queries with similar fields together into a single resulting data set without performing any relational joins (i.e. you want to list one dataset immediately after the other), you will use a UNION query. However, it is notable that these quer...

The BOM (Browser Object Model) contains objects that represent the current browser window and components; objects that model things like history, device's screen, etc The topmost object in BOM is the window object, which represents the current browser window or tab. Document: represents current...

An awk consists of patterns and actions, enclosed in curly brackets, to be taken if a pattern matches. The most basic pattern is the empty pattern, which matches any record. The most basic action is the empty action, which is equivalent to { print }, which is, in turn, equivalent to { print $0 }. If...

The http_build_query() will create a query string from an array or object. These strings can be appended to a URL to create a GET request, or used in a POST request with, for example, cURL. $parameters = array( 'parameter1' => 'foo', 'parameter2' => 'bar', ); $queryString = http_b...

Basic usage If the value of the href-attribute begins with mailto: it will try to open an email client on click: <a href="mailto:[email protected]">Send email</a> This will put the email address [email protected] as the recipient for the newly created email. Cc and ...

When INSERTing, you can use OUTPUT INSERTED.ColumnName to get values from the newly inserted row, for example the newly generated Id - useful if you have an IDENTITY column or any sort of default or calculated value. When programatically calling this (e.g., from ADO.net) you would treat it as a nor...

<PropertyGroup> <!-- Definition of a Property named "TestCondition". A PropertyGroup may also be placed inside a Target. --> <TestCondition>True</TestCondition> </PropertyGroup> <!-- This Target will run after the "Clean" Target, su...

There is a constructor of the same name: DT <- data.table( x = letters[1:5], y = 1:5, z = (1:5) > 3 ) # x y z # 1: a 1 FALSE # 2: b 2 FALSE # 3: c 3 FALSE # 4: d 4 TRUE # 5: e 5 TRUE Unlike data.frame, data.table will not coerce strings to factors by default: sa...

# example data DT = data.table(Titanic) Suppose we only want to see second class: DT[ Class == "2nd" ] # Class Sex Age Survived N # 1: 2nd Male Child No 0 # 2: 2nd Female Child No 0 # 3: 2nd Male Adult No 154 # 4: 2nd Female Adult ...

# example data DT = data.table(Titanic) Suppose we want to see each class only if a majority survived: DT[, if (sum(N[Survived=="Yes"]) > sum(N[Survived=="No"]) ) .SD, by=Class] # Class Sex Age Survived N # 1: 1st Male Child No 0 # 2: 1st Fema...

Match (node_name:node_type {}), (node_name_two:node_type_two {}) CREATE (node_name)-[::edge_name{}]->(node_name_two)

A quick note before actually installing RabbitMQ: Ubuntu 14.04's Erlang packages have issues if you are using SSL with RabbitMQ, so you'll need to install a newer version than what the Ubuntu package maintainers provide, so use the binaries at https://www.erlang-solutions.com/resources/download.html...

Monotonic predicates can be debugged by applying declarative reasoning. In pure Prolog, a programming mistake can lead to one or all of the following phenomena: the predicate incorrectly succeeds in a case where it should fail the predicate incorrectly fails in a case where it should succeed t...

Here are examples of how to use monotonic predicates instead of impure, non-monotonic constructs in your programs: dif/2 is meant to be used instead of non-monotonic constructs like (\=)/2 arithmetic constraints (CLP(FD), CLP(Q) and others) are meant to be used instead of moded arithmetic predi...