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#[macro_use]
extern crate clap;
use clap::App;
fn main() {
// You can use some convenience macros provided by clap to get typed values, so long as the
// type you specify implements std::str::FromStr
//
// This works for both single, and multiple values (multiple values returns a Vec<T>)
//
// There are also two ways in which to get types, those where failures cause the program to exit
// with an error and usage string, and those which return a Result<T,String> or Result<Vec<T>,String>
// respectively. Both methods support single and multiple values.
//
// The macro which returns a Result allows you decide what to do upon a failure, exit, provide a
// default value, etc. You have control. But it also means you have to write the code or boiler plate
// to handle those instances.
//
// That is why the second method exists, so you can simply get a T or Vec<T> back, or be sure the
// program will exit gracefully. The catch is, the second method should *only* be used on required
// arguments, because if the argument isn't found, it exits. Just FYI ;)
//
// The following example shows both methods.
//
// **NOTE:** to use the macros, you must include #[macro_use] just above the 'extern crate clap;'
// declaration in your crate root.
let matches = App::new("myapp")
// Create two arguments, a required positional which accepts multiple values
// and an optional '-l value'
.args_from_usage(
"<seq>... 'A sequence of whole positive numbers, i.e. 20 25 30'
-l [len] 'A length to use, defaults to 10 when omitted'")
.get_matches();
// Here we get a value of type u32 from our optional -l argument.
// If the value provided to len fails to parse, we default to 10
//
// Using other methods such as unwrap_or_else(|e| println!("{}",e))
// are possible too.
let len = value_t!(matches, "len", u32).unwrap_or(10);
println!("len ({}) + 2 = {}", len, len + 2);
// This code loops through all the values provided to "seq" and adds 2
// If seq fails to parse, the program exits, you don't have an option
for v in values_t!(matches, "seq", u32).unwrap_or_else(|e| e.exit()) {
println!("Sequence part {} + 2: {}", v, v + 2);
}
}
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