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class bus_txn;
  rand bit [31:0] addr;
  rand bit [7:0]  len;
  constraint legal_c { len inside {[1:16]}; addr < 32'h1_0000; }
endclass
module tb_tighten_only;
  initial begin
    automatic bus_txn t = new();
    // Tighten: legal AND call-site, so len in [4:16], addr in [0x8000:0xFFFF]
    if (!t.randomize() with { len >= 4; addr >= 32'h8000; })
      $fatal(1, "FAIL: the tightened solve failed");
    if (t.len < 4 || t.len > 16 || t.addr < 32'h8000 || t.addr > 32'hFFFF)
      $fatal(1, "FAIL: len=%0d addr=%h outside the intersection", t.len, t.addr);
    // Contradiction: len==32 meets len in [1:16] nowhere
    if (!t.randomize() with { len == 32; })
      $display("empty intersection: no value satisfies both rules");
    else $fatal(1, "FAIL: len == 32 should contradict legal_c");
    $display("PASS: inline with only tightened the class rules");
    $finish;
  end
endmodule

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class bus_txn;
  rand bit [31:0] addr;
  rand bit [7:0]  len;
  constraint legal_c { len inside {[1:16]}; addr < 32'h1_0000; }
endclass
class my_seq;
  bit [31:0] addr;   // the sequence's own addr shadows the field
  task body(bus_txn t);
    addr = 32'h4000;
    // Bug: both names bind to t.addr, so the rule is t.addr == t.addr
    void'(t.randomize() with { addr == addr; });
    // Fix: local:: skips the object and binds the calling scope
    void'(t.randomize() with { addr == local::addr; });
    if (t.addr != 32'h4000)
      $fatal(1, "FAIL: local::addr did not bind, addr=%h", t.addr);
  endtask
endclass
module tb_scope;
  initial begin
    automatic my_seq s = new();
    automatic bus_txn t = new();
    s.body(t);
    $display("PASS: local::addr pinned t.addr to 4000");
    $finish;
  end
endmodule

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class bus_txn;
  rand bit [31:0] addr;
  rand bit [7:0]  len;
  constraint legal_c { len inside {[1:16]}; addr < 32'h1_0000; }
endclass
class short_bus_txn extends bus_txn;
  constraint short_c { len inside {[1:4]}; }   // still ANDs with legal_c
endclass
module tb_one_off;
  bit [31:0] targets[];   // directed sweep values, sized by the test
  initial begin
    automatic bus_txn t = new();
    targets = new[4];
    foreach (targets[i]) begin
      // Inline: a directed sweep inside one sequence
      void'(t.randomize() with { addr == local::targets[i]; len == 1; });
      if (t.addr != targets[i] || t.len != 1)
        $fatal(1, "FAIL: sweep %0d gave addr=%h len=%0d", i, t.addr, t.len);
    end
    // Inline CANNOT ask for len > 16: that contradicts legal_c,
    // so relaxation needs constraint_mode or a subclass.
    $display("PASS: 4 directed sweep calls hit their targets");
    $finish;
  end
endmodule