Generics can define parameterized items which can’t achieved by parameter override. The following items support generics:

  • function
  • module
  • interface
  • package
  • struct
  • union

Each generic definition has generic parameters (often an uppercase letter is used like T) which can be placed as identifier or expression in the definition. Generic parameters are declarated after item’s identifier with ::<>.

At the usage of generics, actual parameters can be given through ::<>. As the actual parameters, numeric literal and identifier concatenated by :: can be used.

Additionally, the actual parameters should be accessible at the position of the generics declaration. For example, module names can be used as actual parameters because it is accessible through the whole project. On the other hand, local parameters can’t be used as actual parameters in many cases. This is caused by that the local parameters is not accessible from the potision of the generics declaration.

Generic Function

module ModuleA {
    function FuncA::<T> (
        a: input logic<T>,
    ) -> logic<T> {
        return a + 1;

    let _a: logic<10> = FuncA::<10>(1);
    let _b: logic<20> = FuncA::<20>(1);

Generic Module/Interface

module ModuleA {
    inst u0: ModuleB::<ModuleC>;
    inst u1: ModuleB::<ModuleD>;

module ModuleB::<T> {
    inst u: T;

module ModuleC {}
module ModuleD {}

Generic Package

module ModuleA {
    local A: u32 = PackageA::<1>::X;
    local B: u32 = PackageA::<2>::X;

package PackageA::<T> {
    local X: u32 = T;

Generic Struct

module ModuleA {
    type TypeA = i32;

    struct StructA::<T> {
        A: T,

    // local defined type can be used
    // because `TypeA` is accessible at the definition of `StructA`
    var _a: StructA::<TypeA>          ;
    var _b: StructA::<PackageA::TypeB>;
    var _c: StructA::<PackageA::TypeC>;

package PackageA {
    type TypeB = u32;
    type TypeC = u64;