Enum option parsing must be infallible? #5303
Answered
by
epage
stevenengler
asked this question in
Q&A
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|
I'm trying to use an enum as a clap argument. use clap::Parser;
#[derive(Debug, Parser)]
#[command(version)]
pub struct Args {
#[clap(long, default_value_t)]
pub unified: Unified,
}
#[derive(Copy, Clone, Debug)]
pub enum Unified {
Num(u64),
Infinite,
}
impl std::fmt::Display for Unified {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Num(x) => write!(f, "{x}"),
Self::Infinite => write!(f, "infinite"),
}
}
}
impl Default for Unified {
fn default() -> Self {
Self::Num(5)
}
}As expected, this doesn't compile because there's no implementation to convert from string to I don't know what any of that means, but it says it's missing a impl std::str::FromStr for Unified {
type Err = ();
fn from_str(_s: &str) -> Result<Self, Self::Err> {
todo!();
}
}Now we get the same error, except We can try implementing impl<'a> From<&'a str> for Unified {
fn from(_s: &str) -> Self {
todo!();
}
}Now it works. So my question is, does the enum parsing need to infalliable? This means the parsing needs to panic on invalid inputs, which isn't ideal. Are there any alternative ways to use enums with non-unit variants with clap? |
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Answered by
epage
Jan 15, 2024
Replies: 1 comment 1 reply
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Errors are supported but they must be compatible with clap's errors ( |
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1 reply
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Ah okay, thanks! If I do add a impl std::str::FromStr for Unified {
type Err = String;
fn from_str(_s: &str) -> Result<Self, Self::Err> {
todo!();
}
} |
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Answer selected by
stevenengler
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Errors are supported but they must be compatible with clap's errors (
'static + Send + Sync) and must be able to be shown to the user (Display).