Forums > Gen

gen and History in functions

Jun 25 2013 | 4:24 pm

When writing GenExpr code I have found it very useful to have History operators defined in a function like so:

gran_voice(buf, chan, window, pitch, speed, grain_randomness, grain_length, phase) {
    History hold_val(0);
    History win_index(0);
    History buf_index(0);
    History rand_offset(0);



This allows for the functions to carry around an internal state and makes them somewhat quasi-closures. This makes the functions I am defining in a .genexpr library far more portable and easy to deal with. I can see in the exported C++ code the State structure contains these as fields with various numbers appended to them. It would be nice to be able to access these internal History operators in GenExpr but I can’t see a way to do this and I assume it would be difficult based on the way the exported C++ code is setup or would require functors and some changes that might slow things down. Is my assumption correct with this?

Jul 04 2013 | 3:51 pm

Partly. Because it is a closure, each instance of gran_voice() in the GenExpr code will create new History memory in the generated code, hence the auto-naming. However this is partly an implementation detail; e.g. in earlier implementations we generated functor structs. We want to preserve the possibility of changing the implementation in the future too: it’s not clear yet what the optimal implementation is, and thus what kind of interface it could support.

Jul 07 2013 | 9:58 pm

It would be nice if functions were first class values and there was a mechanism for accessing internal history objects but it doesn’t seem very compatible with the current paradigm which has the advantage of seeming to be very fast.

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