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Encapsulation with local and protected: Code Examples

Code Examples for Encapsulation with local and protected.

Code examples

local and protected member declarations

systemverilog
class base_txn;
  local int unsigned txn_id;
  protected rand bit [31:0] addr;

  function new(int unsigned txn_id = 0);
    this.txn_id = txn_id;
  endfunction

  function void set_addr(bit [31:0] a);
    addr = a;
  endfunction

  function bit [31:0] get_addr();
    return addr;
  endfunction
endclass

Seeds the core pattern: local hides strict internals; protected allows controlled inheritance-level visibility.

Derived class can access protected but not local

systemverilog
class base_txn;
  local int unsigned txn_id;
  protected bit [31:0] addr;
endclass

class ext_txn extends base_txn;
  function void tweak();
    addr = 32'hABCD_0001;   // legal: protected in base
    // txn_id = 5;           // illegal: local in base
  endfunction
endclass

Clarifies the visibility boundary between inheritance users and outside users.

Validation through methods instead of public fields

systemverilog
class burst_cfg;
  local int unsigned burst_len;

  function void set_burst_len(int unsigned n);
    if (n inside {[1:256]}) burst_len = n;
    else $fatal(1, "burst_len out of range");
  endfunction

  function int unsigned get_burst_len();
    return burst_len;
  endfunction
endclass

Shows encapsulation as an invariant-preserving API: no external direct write can bypass checks.

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