Namespaces

Namespaces group related types and POUs under a common name, preventing name clashes and making large projects easier to navigate.

Declaring a namespace

A namespace is declared with NAMESPACE … END_NAMESPACE and contains type declarations, functions, function blocks, classes, interfaces and — nested — further namespaces.

NAMESPACE Drives
    FUNCTION_BLOCK Motor
        ...
    END_FUNCTION_BLOCK

    TYPE
        Direction : (FORWARD, REVERSE);
    END_TYPE
END_NAMESPACE

Internal namespaces

Prefix the declaration with INTERNAL to restrict the namespace’s contents to the project that declares it (it is not exported for use by other projects / libraries).

NAMESPACE INTERNAL Diagnostics
    ...
END_NAMESPACE

Nested namespaces

Namespaces can be nested directly:

NAMESPACE Plant
    NAMESPACE Drives
        FUNCTION_BLOCK Motor ... END_FUNCTION_BLOCK
    END_NAMESPACE
END_NAMESPACE

Qualified names

Refer to a member of a namespace by its dotted path. Nested namespaces are chained with ..

VAR
    m1 : Drives.Motor;
    m2 : Plant.Drives.Motor;
    dir : Drives.Direction := Drives.Direction#FORWARD;
END_VAR

The USING directive

USING imports one or more namespaces so their members can be referenced unqualified. It may appear at the top of a POU or namespace, before the declarations.

USING Drives, Plant.Drives;

FUNCTION_BLOCK Conveyor
VAR
    m : Motor;          // resolves to Drives.Motor via USING
END_VAR
END_FUNCTION_BLOCK

Multiple namespaces are separated by commas in a single USING, or you can write several USING directives.

Note

A fully-qualified name always works regardless of USING. Reach for a qualified name when two imported namespaces both define a member with the same simple name, to make the reference unambiguous.