<details><summary>Combinatoric example</summary>
```no_run
#[derive(Debug, Clone)]
pub struct Options {
number: u32,
}
pub fn options() -> OptionParser<Options> {
let number = long("number").argument::<u32>("N").guard(
|n| *n <= 10,
"Values greater than 10 are only available in the DLC pack!",
);
construct!(Options { number }).to_options()
}
fn main() {
println!("{:?}", options().run())
}
```
</details>
<details><summary>Derive example</summary>
```no_run
fn dlc_check(number: &u32) -> bool {
*number <= 10
}
const DLC_NEEDED: &str = "Values greater than 10 are only available in the DLC pack!";
#[derive(Debug, Clone, Bpaf)]
#[bpaf(options)]
pub struct Options {
#[bpaf(argument("N"), guard(dlc_check, DLC_NEEDED))]
number: u32,
}
fn main() {
println!("{:?}", options().run())
}
```
</details>
<details><summary>Output</summary>
`guard` don't make any changes to generated `--help` message
<div class='bpaf-doc'>
$ app --help<br>
<p><b>Usage</b>: <tt><b>app</b></tt> <tt><b>--number</b></tt>=<tt><i>N</i></tt></p><p><div>
<b>Available options:</b></div><dl><dt><tt><b> --number</b></tt>=<tt><i>N</i></tt></dt>
<dt><tt><b>-h</b></tt>, <tt><b>--help</b></tt></dt>
<dd>Prints help information</dd>
</dl>
</p>
<style>
div.bpaf-doc {
padding: 14px;
background-color:var(--code-block-background-color);
font-family: "Source Code Pro", monospace;
margin-bottom: 0.75em;
}
div.bpaf-doc dt { margin-left: 1em; }
div.bpaf-doc dd { margin-left: 3em; }
div.bpaf-doc dl { margin-top: 0; padding-left: 1em; }
div.bpaf-doc { padding-left: 1em; }
</style>
</div>
You can use guard to set boundary limits or perform other checks on parsed values.
Parser accepts numbers below 10
<div class='bpaf-doc'>
$ app --number 5<br>
Options { number: 5 }
</div>
And fails with the error message on higher values:
<div class='bpaf-doc'>
$ app --number 11<br>
<b>Error:</b> <b>11</b>: Values greater than 10 are only available in the DLC pack!
<style>
div.bpaf-doc {
padding: 14px;
background-color:var(--code-block-background-color);
font-family: "Source Code Pro", monospace;
margin-bottom: 0.75em;
}
div.bpaf-doc dt { margin-left: 1em; }
div.bpaf-doc dd { margin-left: 3em; }
div.bpaf-doc dl { margin-top: 0; padding-left: 1em; }
div.bpaf-doc { padding-left: 1em; }
</style>
</div>
But if function inside the parser fails - user will get the error back unless it's handled
in some way
<div class='bpaf-doc'>
$ app --number ten<br>
<b>Error:</b> couldn't parse <b>ten</b>: invalid digit found in string
<style>
div.bpaf-doc {
padding: 14px;
background-color:var(--code-block-background-color);
font-family: "Source Code Pro", monospace;
margin-bottom: 0.75em;
}
div.bpaf-doc dt { margin-left: 1em; }
div.bpaf-doc dd { margin-left: 3em; }
div.bpaf-doc dl { margin-top: 0; padding-left: 1em; }
div.bpaf-doc { padding-left: 1em; }
</style>
</div>
</details>