implement opt_get() method call on Matches. #70
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prataprc
commented
May 22, 2018
prataprc
commented
- more tolerant than opt_default.
- folds str::parse() on the argument and returns Result<T,E>.
src/lib.rs
Outdated
| /// Similar to opt_default, except the two differences. Instead of | ||
| /// returning None when option was not present, return `def`. Instead of | ||
| /// returning &str slice return valued of type T parsed using str::parse(). | ||
| pub fn opt_get<T>(&self, nm: &str, def: T) |
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This looks like a good addition to me! What do you think about having two methods here:
pub fn opt_get<T>(&self, nm: &str) -> Result<Option<T> T::Err>;
pub fn opt_get_default<T>(&self, nm: &str, def: T) -> Result<T: T::Err>;so that we can still use this method in cases where there isn't an obvious default to use?
The Result<Option> signature is a little weird, but chances are you'd blow up on the result, and branch on the option:
match matches.opt_get("name")? {
Some(opt) => { ... },
None => { ... }
}Or maybe:
let opt = matches.opt_get("name").unwrap_or_else(|e| {
println!("invalid value for `name`: {}", e);
...
process::exit(1)
});What do you think?
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By T::Err in the Result<> did you mean ::Err ? Or is that
something new ?
so that we can still use this method in cases where there isn't an obvious
default to use?
In these cases won't opts_str, opt_str and opt_default be useful ? I haven't
really used getopts much, so I am not able to judge which is more ergonomic ..
Cheers,
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Ah, by T::Err I mean the associated error type on the FromStr trait, like you have currently. We should actually be able to just say T::Err instead of <T as FromStr>::Err because all we know about T from the where clause is that it implements FromStr.
If you use opt_str you'll still need to do the FromStr conversion yourself, so having opt_get without a default is closer to how opt_str works already.
* more tolerant than opt_default. * folds str::parse() on the argument and returns Result<T,E>.
