iverilog/docs/param-classes.md

Tier A #1 — Parameterized classes

Track: muhammadjawadkhan/iverilog-uvm only (feat/param-classes). Do not open PRs to steveicarus/iverilog for this work.

Goal

Support SystemVerilog parameterized classes needed for Accellera-shaped UVM (uvm_*#(T), config_db, etc.):

class C #(type T = int, parameter int W = 8);
  // ...
endclass

C#(byte) c;   // explicit specialization — not done yet

What landed (ANSI parameter ports + defaults)

Grammar (parse.y)

class_declaration now pushes the class scope before the optional #(...) parameter port list (same idea as modules), then applies extends:

1. K_virtual_opt K_class lifetime_opt identifier_name → start class / typedef (pform_start_class_declaration with base type deferred).
2. module_parameter_port_list_opt — reuse the existing module ANSI parameter-port grammar so type T = int, parameter int W = 8, etc. land in the class LexicalScope.
3. class_declaration_extends_opt ';' → pform_set_class_extends(...).
4. class items / endclass as before.

Pform (pform_pclass.cc / pform.h)

• pform_set_class_extends — fills base_type / base_args on the current class after the parameter port list (replacing the old path that passed extends into pform_start_class_declaration before #(...) could exist).
• Related: pform_start_class_declaration, pform_end_class_declaration, property helpers unchanged in role.

With defaults present, a bare instance like box b; elaborates using those defaults.

Smoke example

examples/param_classes/box_default.sv — class box #(type T = int, parameter int W = 8); constructed and used without an explicit #() override. Companion regression: plain_class.sv.

iverilog -g2012 -o box_default.vvp examples/param_classes/box_default.sv && vvp box_default.vvp
# expect: PASS box_default ...

TODO

• Explicit specialization / overrides: C#(byte), C#(byte, 16), named overrides — parse, elaborate a specialized class type, and wire instances to it.
• Inheritance + parameters interactions as needed by UVM base classes.
• Broader ivtest coverage beyond the local smoke examples.

Status pointer

See STATUS.md (Parameterized classes row) and ROADMAP.md Tier A item 1.