select

static VALUE
fgdbm_select(VALUE obj)
{
    VALUE new = rb_ary_new();
    GDBM_FILE dbm;
    struct dbmdata *dbmp;
    VALUE keystr;

    GetDBM2(obj, dbmp, dbm);
    for (keystr = rb_gdbm_firstkey(dbm); RTEST(keystr);
         keystr = rb_gdbm_nextkey(dbm, keystr)) {
        VALUE assoc = rb_assoc_new(keystr, rb_gdbm_fetch2(dbm, keystr));
        VALUE v = rb_yield(assoc);

        if (RTEST(v)) {
            rb_ary_push(new, assoc);
        }
        GetDBM2(obj, dbmp, dbm);
    }

    return new;
}