How to limit an CLI argument to an enum? [duplicate]

Question

While learning Rust and in an attempt to do something useful, I'm looking to craft a SAFE API call for DNS:Add service. The API is well defined and should by rights be a simple PUT request, the body of which is a number of strings and one variable that is limited to two options.

I've looked to define a struct and enum for the body of the put with its real limits, rather than just using strings; as I expect defining close the reality, is better practice.

I think I must be close but then have a mismatch, trying to limit input to an enum. The third argument should be only 'drive' or 'app' as RootPathVariant.

So, I'm looking to assign the root_path with a match of arguments=arg[2] but atm the left-side of the match is &'static str, which is wrong where it wants a String.

enum is defined:

pub enum RootPathVariant { App, Drive }

impl RootPathVariant {
    pub fn as_str(&self) -> &str {
        match self {
            &RootPathVariant::App => "app",
            &RootPathVariant::Drive => "drive",
        }
    }
}

How should I put the left side of this match, to only accept content of that enum?

let mut root_path: RootPathVariant = RootPathVariant::Drive;
match args[2].to_string() {
    "drive" => { root_path = RootPathVariant::Drive },
    "app" => { root_path = RootPathVariant::App },
    _ => { println!( "Error: root_path not [drive | app]");  return }
};

let put_body = AddServiceBody {
    long_Name: args[0],
    service_Name: args[1],
    root_Path: root_path,
    service_Home_Dir_Path: args[3]
};

Thanks for any help!

You can use string.as_ref() to get &str from a String and then use it in a match. But what is the type of args? to_string() may be unnecessary if you already have &str. — Pavel Strakhov
– Pavel Strakhov, Commented Oct 23, 2016 at 2:10
Please add the exact error message and a minimal reproducible example. Then you are more likely to get any answers :) — Lukas Kalbertodt
– Lukas Kalbertodt, Commented Oct 23, 2016 at 7:43
@Pavel Strakhov the type of args follows simple from Cargo:getopts as a Vec<String>. I missed the obvious option to match args[2].as_str() which appears to work! — David Brown
– David Brown, Commented Oct 23, 2016 at 9:45
I'm seconding @LukasKalbertodt's point about an MCVE. For example, this question has nothing to do with an enum. I'd bet that your code looks like this. — Shepmaster
– Shepmaster, Commented Oct 23, 2016 at 13:15

David Brown · Accepted Answer · 2016-10-23 09:47:29Z

1

Noting the answer looks to be to match args[2].as_str()!

answered Oct 23, 2016 at 9:47

David Brown

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How to limit an CLI argument to an enum? [duplicate]

enum is defined:

How should I put the left side of this match, to only accept content of that enum?

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enum is defined:

How should I put the left side of this match, to only accept content of that enum?

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