Re: C++ vs. GCPRO

Martin Buchholz <martin(a)xemacs.org&gt; writes: [My first post seems missing from the list. Sorry if you see this twice] Here is something I prepared earlier (ahem). All these structs would be typedef'ed in a real use of course. I think you can do this checking as long as you allow about 6 or so different types that under C would all just be the same thing. g++ -c gcpro.C gcpro.C: In function `void incorrect()': gcpro.C:74: conversion from `rv_lispobj' to non-scalar type `funarg_lispobj' requested Here is gcpro.C typedef unsigned int lispobj_internal; struct funarg_lispobj; struct stack_lispobj; /* Function returnvalues */ struct rv_lispobj { lispobj_internal i; // Here would come contructurs from most lisp_obj }; struct ungcable_lispobj { lispobj_internal i; ungcable_lispobj(unsigned int in) { i = in; }; private: ungcable_lispobj(); }; /* Function arguments for functions that cannot GC */ struct nogcarg_lispobj { lispobj_internal i; nogcarg_lispobj(const struct ungcable_lispobj in); nogcarg_lispobj(const struct funarg_lispobj in); nogcarg_lispobj(const struct stack_lispobj in); nogcarg_lispobj(const struct rv_lispobj in); }; struct funarg_lispobj { lispobj_internal i; funarg_lispobj(const struct stack_lispobj in); // Would check in.gcprod_flag // Note the missing contructor from rv_lispobj; // Note the missing contructor from nogcarg_lispobj; }; struct stack_lispobj { lispobj_internal i; bool gcpro_flag; stack_lispobj() { gcpro_flag = false; }; stack_lispobj(const struct rv_lispobj in) { i = in.i; }; }; struct ungcable_lispobj zero(0); struct rv_lispobj Fcons(struct nogcarg_lispobj car, struct nogcarg_lispobj cdr); // Can GC struct rv_lispobj bar(struct funarg_lispobj arg); void correct1() { stack_lispobj obj = Fcons(zero,zero); obj.gcpro_flag = true; // Would be part of GCPRO; bar(obj); } void correct2() { Fcons(Fcons(zero,zero),zero); } void incorrect() { bar(Fcons(zero,zero)); }