DBM#reject!

static VALUE
fdbm_delete_if(VALUE obj)
{
    datum key, val;
    struct dbmdata *dbmp;
    DBM *dbm;
    VALUE keystr, valstr;
    VALUE ret, ary = rb_ary_tmp_new(0);
    int status = 0;
    long i, n;

    fdbm_modify(obj);
    GetDBM2(obj, dbmp, dbm);
    n = dbmp->di_size;
    dbmp->di_size = -1;

    for (key = dbm_firstkey(dbm); key.dptr; key = dbm_nextkey(dbm)) {
        val = dbm_fetch(dbm, key);
        keystr = rb_str_new(key.dptr, key.dsize);
        OBJ_FREEZE(keystr);
        valstr = rb_str_new(val.dptr, val.dsize);
        ret = rb_protect(rb_yield, rb_assoc_new(rb_str_dup(keystr), valstr), &status);
        if (status != 0) break;
        if (RTEST(ret)) rb_ary_push(ary, keystr);
        GetDBM2(obj, dbmp, dbm);
    }

    for (i = 0; i < RARRAY_LEN(ary); i++) {
        keystr = RARRAY_AREF(ary, i);
        key.dptr = RSTRING_PTR(keystr);
        key.dsize = (DSIZE_TYPE)RSTRING_LEN(keystr);
        if (dbm_delete(dbm, key)) {
            rb_raise(rb_eDBMError, "dbm_delete failed");
        }
    }
    if (status) rb_jump_tag(status);
    if (n > 0) dbmp->di_size = n - RARRAY_LEN(ary);
    rb_ary_clear(ary);

    return obj;
}