I am new to Rust and clap, so I apologize if some of the terminology I use in my question isn't correct.
I am writing a CLI tool in Rust which takes a parameter called property_name. This property_name has a list of possible values, and I want clap to only allow these possible values and reject anything else.
My code builds a vector of these values from other data. For simplicity, I've replaced that code with just a simple vector declaration to illustrate my issue. Here is the code:
let property_values = vec!["one", "two", "three"];
#[derive(Parser, Debug)]
#[clap(author, version, about, long_about = None)]
struct Args {
#[structopt(short('n'), long, required=true, value_parser, possible_values=property_values)]
property_name: Option<String>
}
This produces the following error:
error[E0434]: can't capture dynamic environment in a fn item
--> src\main.rs:114:83
|
114 | #[structopt(short('n'), long, required=true, value_parser, possible_values=property_values)]
| ^^^^^^^^^^^^^^^
|
= help: use the `|| { ... }` closure form instead
After reading about the error message and using Google searches, I haven't been able to understand the proper fix. The example fixes given don't seem to help, like using a closure (this is likely not quite the right syntax?):
#[structopt(short('n'), long, required=true, value_parser, possible_values=|property_values|property_values)]
This led to different compiler errors:
--> src\main.rs:114:67
|
114 | #[structopt(short('n'), long, required=true, value_parser, possible_values=|property_values|property_values)]
| ^^^^^^^^^^^^^^^ ----------------- consider calling this closure
| |
| `[closure@src\main.rs:114:83: 114:100]` is not an iterator
|
= help: the trait `Iterator` is not implemented for `[closure@src\main.rs:114:83: 114:100]`
= note: required because of the requirements on the impl of `IntoIterator` for `[closure@src\main.rs:114:83: 114:100]`
I could investigate iterators, and maybe that is the proper fix, but I decided to ask my question here before going further down that path.
Also, if I put the possible values directly into the declaration as an array, like this, it all works as expected:
#[structopt(short('n'), long, required=true, value_parser, possible_values=["one", "two", "three"])]
However, since I am building this vector dynamically at run-time, I can't use this solution.
I'm sure that there's something fundamental that I'm missing, but I don't have enough experience and knowledge with Rust to know where to look to learn how to do this. Would a kind soul point me toward a blog post, documentation, or code sample that could help me understand how to do this?
