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Why [ ] operator is not overloaded for sc_signal ?

Roman Popov

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A follow-up question for



Why square brakets are not overloaded for sc_signal class?  In case underling datatype allows bit-level access, it seems it would be handy to allow it for signals?


Looks like there is no technical limitation to do this, here is an example:

#include <systemc.h>

template< class T, sc_writer_policy POL = SC_DEFAULT_WRITER_POLICY >
struct my_sc_signal : public sc_signal<T, POL> {
    typedef my_sc_signal<T,POL>          this_type;
    typedef sc_signal<T, POL>            base_type;

    explicit my_sc_signal( const char* name_)  : base_type( name_ ){}

    struct signal_writer_helper {
        signal_writer_helper (this_type &s, size_t i) : sig(s), id(i) {}

        template <typename AT>
        void operator = ( const AT& val_ )
            bool value_changed = !( sig.m_cur_val[id] == val_ );

            sig.m_new_val[id] = val_;
            if( value_changed )

        this_type &sig;
        size_t id;


    signal_writer_helper operator [](size_t i) {
        return signal_writer_helper(*this, i);


SC_MODULE(test) {

    static const int BUS_WIDTH = 10;
    my_sc_signal<sc_uint<BUS_WIDTH> > test_sig{"test_sig"};

    SC_CTOR(test) {
        sensitive << test_sig;

    void master_thread() {
        for (int i = 0; i < BUS_WIDTH; ++i) {
            test_sig[i] = 1;
            wait(1, SC_NS);

        for (int i = 0; i < BUS_WIDTH; ++i) {
            test_sig[i] = 1;
            wait(1, SC_NS);


    void slave_method() {
        cout << "New signal value is: " << test_sig.read() << endl;


int sc_main(int argc, char *argv[]) {

    test test_inst("test_inst");
    return 0;


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There is an ASSIGN implementation proposal in:




So with bit level access to sc_signals I can imagine something like:


ASSIGN( addr_sig, a_sel_sig = addr_sig[0] );

ASSIGN( addr_sig, b_sel_sig = addr_sig[1] );

ASSIGN( addr_sig, c_sel_sig = addr_sig[2] );


or even

ASSIGN( addr_sig[0], a_sel_sig = addr_sig[0] );

ASSIGN( addr_sig[1], b_sel_sig = addr_sig[1] );

ASSIGN( addr_sig[2], c_sel_sig = addr_sig[2] );

if sc_signal[] returns something with event capabilities
Highly desired for Synthesizable SystemC.
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