# XO1201: not available without a garbage collector

`xo build --no-gc` (also `xo run`, `xo test`, and `xo check`) selects a native backend (arm64 on arm64 hosts, LLVM otherwise), whose memory is reference counted instead of collected. Before any code is generated, a check reports every construct, std API, or effect the native backends do not support, at the call site, naming the feature. The message says whether support is planned (the program will build once the native backends grow it; until then build without `--no-gc`) or impossible: code from a `use go` package needs Go's runtime and garbage collector, so it can never run in a native build. The check is derived from what the native code generator supports, so a program it accepts builds. See core 10.1 and decision 0083.

## Example

```xo
use go "strings"

fn main(os: Os) uses go {
  os.stdio.println(strings.to_upper("hi"))
}
```

## Fix

```xo
fn main(os: Os) {
  os.stdio.println("hi".to_upper())
}
```

Run `xo explain XO1201` for this text in a terminal, or see
[section 10.6 of the specification](../../spec/core/#106-diagnostic-codes).