Presentation in README.md

README.md

@@ -1,9 +1,86 @@
 # StructOpt [![Build status](https://travis-ci.org/TeXitoi/structopt.svg?branch=master)](https://travis-ci.org/TeXitoi/structopt) [![](https://img.shields.io/crates/v/structopt.svg)](https://crates.io/crates/structopt) [![](https://docs.rs/structopt/badge.svg)](https://docs.rs/structopt)
 
-Parse command line argument by defining a struct.
+Parse command line argument by defining a struct.  It combines [clap](https://crates.io/crates/clap) with custom derive.
-
-Work in progress.
 
 ## Documentation
 
 Find it on [Docs.rs](https://docs.rs/structopt)
+
+## Example
+
+```rust
+extern crate structopt;
+#[macro_use]
+extern crate structopt_derive;
+
+use structopt::StructOpt;
+
+#[derive(StructOpt, Debug)]
+#[structopt(name = "example", about = "An example of StructOpt usage.")]
+struct Opt {
+    /// A flag, true if used in the command line.
+    #[structopt(short = "d", long = "debug", help = "Activate debug mode")]
+    debug: bool,
+
+    /// An argument of type float, with a default value.
+    #[structopt(short = "s", long = "speed", help = "Set speed", default_value = "42")]
+    speed: f64,
+
+    /// Needed parameter, the first on the command line.
+    #[structopt(help = "Input file")]
+    input: String,
+
+    /// An optional parameter, will be `None` if not present on the
+    /// command line.
+    #[structopt(help = "Output file, stdout if not present")]
+    output: Option<String>,
+}
+
+fn main() {
+    let opt = Opt::from_args();
+    println!("{:?}", opt);
+}
+```
+
+Using this example:
+```
+$ ./example
+error: The following required arguments were not provided:
+    <input>
+
+USAGE:
+    example [FLAGS] [OPTIONS] <input> [ARGS]
+
+For more information try --help
+$ ./example --help
+example 0.0.0
+Guillaume Pinot <texitoi@texitoi.eu>
+An example of StructOpt usage.
+
+USAGE:
+    example [FLAGS] [OPTIONS] <input> [ARGS]
+
+FLAGS:
+    -d, --debug      Activate debug mode
+    -h, --help       Prints help information
+    -V, --version    Prints version information
+
+OPTIONS:
+    -s, --speed <speed>    Set speed [default: 42]
+
+ARGS:
+    <input>     Input file
+    <output>    Output file, stdout if not present
+$ ./example foo
+Opt { debug: false, speed: 42, input: "foo", output: None }
+$ ./example -ds 1337 foo bar
+Opt { debug: true, speed: 1337, input: "foo", output: Some("bar") }
+```
+
+## Why
+
+I use [docopt](https://crates.io/crates/docopt) since  long time. I really like the fact that you have a structure with the parsed argumentThat's like going back to the : no need to convert `String` to `f64`, no useless `unwrap`. But in another hand, I don't like to write by hand the usage string. That's like going back to the golden age of WYSIWYG editors.
+
+Today, the new standard to read command line arguments in Rust is [clap](https://crates.io/crates/clap).  This library is so feature full! But I think there is one downside: even if you can validate arument, expressing that an argument is required, you still need to transform something looking like a hashmap of string vectors to something useful for your application.
+
+Now, there is stable custom derive. Thus I can add to clap the automatic conversion that I miss. Here is the result.