# XO0402: type arguments cannot be inferred

A generic function's type parameter was determined by nothing: not the arguments, the expected type, or later use. Write the type argument explicitly (`json.decode[Int](b)`), or give the result an expected type. See core 2.7.

## Example

```xo
use std/json

fn f(b: Bytes) -> Int {
  let _ = json.decode(b).ok()
  1
}
```

## Fix

```xo
use std/json

fn f(b: Bytes) -> Int {
  let _ = json.decode[Int](b).ok()
  1
}
```

Run `xo explain XO0402` for this text in a terminal, or see
[section 10.6 of the specification](../../spec/core/#106-diagnostic-codes).