1 files changed, 36 insertions, 0 deletions
diff --git a/structopt/examples/keyvalue.rs b/structopt/examples/keyvalue.rs
new file mode 100644
index 0000000..12ce6fc
--- /dev/null
+++ b/structopt/examples/keyvalue.rs
@@ -0,0 +1,36 @@
+//! How to parse "key=value" pairs with structopt.
+
+use std::error::Error;
+use structopt::StructOpt;
+
+/// Parse a single key-value pair
+fn parse_key_val<T, U>(s: &str) -> Result<(T, U), Box<dyn Error>>
+where
+    T: std::str::FromStr,
+    T::Err: Error + 'static,
+    U: std::str::FromStr,
+    U::Err: Error + 'static,
+{
+    let pos = s
+        .find('=')
+        .ok_or_else(|| format!("invalid KEY=value: no `=` found in `{}`", s))?;
+    Ok((s[..pos].parse()?, s[pos + 1..].parse()?))
+}
+
+#[derive(StructOpt, Debug)]
+struct Opt {
+    // number_of_values = 1 forces the user to repeat the -D option for each key-value pair:
+    // my_program -D a=1 -D b=2
+    // Without number_of_values = 1 you can do:
+    // my_program -D a=1 b=2
+    // but this makes adding an argument after the values impossible:
+    // my_program -D a=1 -D b=2 my_input_file
+    // becomes invalid.
+    #[structopt(short = "D", parse(try_from_str = parse_key_val), number_of_values = 1)]
+    defines: Vec<(String, i32)>,
+}
+
+fn main() {
+    let opt = Opt::from_args();
+    println!("{:?}", opt);
+}