Using Microsoft .NET Search Path

Using (Microsoft .NET Search Path)

⎕USING

⎕USING specifies a list of Microsoft .NET Namespaces that are to be searched for a reference to a .NET class. ⎕USING has Namespace scope.

⎕USING is a vector of character vectors each element of which contains 1 or 2 comma-delimited strings. The first string specifies the name of a .NET namespace; the second specifies the pathname of an assembly file. This may be a full pathname or a relative one, but must include the file extension (.dll). If just the file name is specified, it is assumed to be located in the standard .NET Framework directory that was specified when the .NET Framework was installed (e.g. C:\Windows\Microsoft.NET\Framework64\v4.0.30319)

It is convenient to treat .NET namespaces and assemblies in pairs. For example:

⎕USING←'System,mscorlib.dll'
  ⎕USING,←⊂'System.Windows.Forms,System.Windows.Forms.dll'  ⎕USING,←⊂'System.Drawing,System.Drawing.dll'

Note that because Dyalog APL automatically loads mscorlib.dll (which contains the most commonly used classes in the System Namespace), it is not actually necessary to specify it explicitly in ⎕USING.

⎕USING has Namespace scope, i.e. each Dyalog APL Namespace, Class or Instance has its own value of ⎕USING that is initially inherited from its parent space but which may be separately modified. ⎕USING may also be localised in a function header, so that different functions can declare different search paths for .NET namespaces/assemblies.

If ⎕USING is empty (⎕USING←0⍴⊂''), APL will not search for .NET classes in order to resolve names which would otherwise give a VALUE ERROR.

Assigning a simple character vector to ⎕USING is equivalent to setting it to the enclose of that vector. The statement (⎕USING←'') does not empty ⎕USING, it sets it to a single empty element, which gives access to mscorlib.dll and the Bridge DLL without a namespace prefix.

Notes

The value of ⎕USING is only used when an object is instantiated. Changing the value of ⎕USING has no effect on objects that have already been instantiated in the active workspace.
When a workspace containing .Net objects is saved, the names of the Net objects are saved with it but they are not automatically re-instantiated when the workspace is loaded or copied. A reference to such an orphaned object will report (NULL).
Some functionality might work with .NET Framework or .NET Core but not both, for example, SharpPlot requires the .NET Framework and does not work with .NET Core

Examples:

  ⎕USING←'System'
  ]display ⎕USING
.→---------.
| .→-----. |
| |System| |
| '------' |
'∊---------'

⎕USING,←⊂'System.Windows.Forms,System.Windows.Forms.dll'
⎕USING,←⊂'System.Drawing,System.Drawing.dll'

An Assembly may contain top-level classes which are not packaged into .NET Namespaces. In this case, you omit the Namespace name. For example:

  ⎕USING←,⊂',.\LoanService.dll'