array.c:1777
static VALUE
ary_make_hash(ary1, ary2)
    VALUE ary1, ary2;
{
    VALUE hash = rb_hash_new();
    long i;

    for (i=0; i<RARRAY(ary1)->len; i++) {
	rb_hash_aset(hash, RARRAY(ary1)->ptr[i], Qtrue);
    }
    if (ary2) {
	for (i=0; i<RARRAY(ary2)->len; i++) {
	    rb_hash_aset(hash, RARRAY(ary2)->ptr[i], Qtrue);
	}
    }
    return hash;
}
