Namespaces

Namespaces are used as a mechanism to prevent naming conflicts when multiple people are working on a design. While ACT can be used without any namespaces (in which case everything is defined and created in the default namespace Global), most large designs will contain structure that can be used to keep the ACT files clean and modular.

A namespace is created by using the namespace construct.

namespace lib {
...
export defproc buffer (a1of2? l; a1of2! r) { ... }
...
}

The process buffer has been created in the namespace lib, and it's fully qualified name is ::lib::buffer. This syntax is similar to the one used by C++.

An ACT type or instance is first evaluated in the current namespace; if it doesn't exist in the current namespace, then the global namespace is searched next.

A namespace typically contains user-defined types. By default, these types are only visible within the current namespace. To allow a type to be visible in any other namespace, it must be prefaced by the export keyword (as above).

A namespace can also contain another namespace. However, these namespaces do not have special privileges. An example of nested namespaces is shown below.

namespace datapath {
    export defproc bus_interface(...) { ... }
    namespace adder {
      export defproc alu(...) {
        bus_interface b;
      }
    }
    ...
}

Nesting does not give a namespace special permissions; if the bus_interface definition was not exported, then the namespace adder within it would not be able to reference bus_interface. However, notice that the type bus_interface within alu did not require its fully qualified name, due to the fact that the definition is in scope due to nesting.

alu cannot be referenced from the global namespace using datapath::adder::alu. Although alu is exported from the namespace datapath::adder, the export directive only exports the definition one level up. To export this another level out, the entire namespace adder can be exported as follows:

namespace datapath {
    export defproc bus_interface(...) { ... }
    export namespace adder {
      export defproc alu(...) {
        bus_interface b;
      }
    }
    ...
}

Now datapath::adder::alu can be accessed from the global namespace.

Namespace globals are instances that are defined outside any type definition. While the Global namespace can have any instances or other constructs used to construct circuits, other namespaces can only have global data types or channels—i.e. no circuits.