Questions tagged [using]

In the C# language, the using keyword is employed in two different contexts, as a Directive and a Statement.

The using directive is used to qualify namespaces and create namespace or type aliases.

using System.Text;
using Project = PC.MyCompany.Project;

The using statement provides a convenient syntax that ensures the correct use of IDisposable objects.

using (MyTypeImplementingIDisposable myInstance)) 
{
    // Do something with myInstance
}

Beginning with C# 8.0, you can use the alternative syntax that doesn't require braces

using var myInstance = new MyTypeImplementingIDisposable(...);
// Do something with myInstance

In the VB.NET language the Using keyword is used only as a Statement and provides the same features as the C# language:

Using sr As New StreamReader(filename)
    ' read the sr stream
End Using

In Haxe, the using keyword allows pseudo-extending existing types without modifying their source (syntactical sugar). It is achieved by declaring a static method with a first argument of the extending type and then bringing the defining class into context through using.

using StringTools;

// works because of the `using`:
var myEncodedString = "Haxe is great".replace("great", "awesome");
// Without the using one should type this: 
var myEncodedString = StringTools.replace("Haxe is great", "great", "awesome");

In gnuplot, the using qualifier allows specific columns in a datafile to be specified, for plotting and fitting.

In C++, the using keyword can be used in 3 ways;

1. using declarations

   using std::swap;

2. using directives

   using namespace std;

3. type alias and alias template declaration (since C++11); similar to typedef

   template <class CharT> using mystring = std::basic_string<CharT,std::char_traits<CharT>>;