id	summary	reporter	owner	description	type	status	priority	component	version	resolution	keywords	cc
207	Safe const variations are not considered for assertion satisfaction	mlbrooks		"Assertion satisfaction is invariant in the function type, but it should be cotravariant in the function's parameters and covariant in the function's returns:

{{{
A function that consumes a const            reference does not satisfy an assertion for a function that consumes a mutation-allowed reference
A function that produces a mutation-allowed reference does not satisfy an assertion for a function that produces a const            reference
}}}

{{{
#ifndef QPROD
#define QPROD
#endif

#ifndef QCONS
#define QCONS
#endif

forall( | { void        helpConsume( QCONS int * );
            QPROD int * helpProduce(             ); } )
void f() {
    int copy = * helpProduce();
    helpConsume( & copy );
}

void helpConsume(int * x) {
    printf( ""got %d\n"", *x );
}

int *helpProduce() {
    static int theVal = 17;
    return & theVal;
}

int main() {
    f();
}
}}}

expected -DQPROD=const, expected -DCONS=const, actual plain: compile succeeds; program prints ""got 17""

actual -DQPROD=const: No alternatives with satisfiable assertions for Applying ... f ... Could not satisfy assertion: helpProduce

actual -DQCONS=const: No alternatives with satisfiable assertions for Applying ... f ... Could not satisfy assertion: helpConsume

A practical example occurs in the sout ?|? treatment of tuples.  The intuition is if a type T is has `sout | T` then by that it also has `sout | [ ... T ... ]`.

We want and have `sout | const char *`.   It is and should be usable as `sout | char *`.  It is and should be usable to satisfy `sout | [ ... const char * ...]`.  It should be, but by this bug is not, usable to satisfy `sout | [ ... char * ...]`.

{{{
int main() {
    sout | ""one"";
    sout | 2;
  #ifdef WORKAROUND
    sout | [ ( const char * ) ""three"", 4 ];
  #else
    sout | [                  ""three"", 4 ];
  #endif
}
}}}

expected plain, actual -DWORKAROUND: compiles and runs with
{{{
one
2
three, 4
}}}

actual plain: No alternatives with satisfiable assertions for Applying untyped:  Name: ?|?  to:  Name: sout,  Untyped Tuple ..."	enhancement	new	minor	cfa-cc	1.0