Updated runner example (#129)

examples/runner/main.rs

@@ -4,24 +4,44 @@ use ixa::ContextPeopleExt;
 
 #[derive(Args, Debug)]
 struct CustomArgs {
+    // Example of a boolean argument.
+    // --say-hello       custom_args.say_hello is true
+    // (nothing)         custom_args.say_hello is false
+    #[arg(long)]
+    say_hello: bool,
+
+    // Example of an optional argument with a required value
+    // -p 12            custom_args.starting_population is Some(12)
+    // -p               This is invalid; you have to pass a value.
+    // (nothing)        custom_args.starting_population is None
     #[arg(short = 'p', long)]
     starting_population: Option<u8>,
 }
 
 fn main() {
+    // The runner reads arguments from the command line.
+    // args refer to `BaseArgs` (see runner.rs for all available args)
+    // custom_args are optional for any arguments you want to define yourself.
+    //
     // Try running the following:
     // cargo run --example runner -- --seed 42
     // cargo run --example runner -- --starting-population 5
     // cargo run --example runner -- -p 5 --debugger
     let context = run_with_custom_args(|context, args, custom_args: Option<CustomArgs>| {
         println!("Setting random seed to {}", args.random_seed);
 
-        // If an initial population was provided, add each person
-        if let Some(custom_args) = custom_args {
-            if let Some(population) = custom_args.starting_population {
-                for _ in 0..population {
-                    context.add_person(()).unwrap();
-                }
+        // As long as you specified a custom type in the signature (CustomArgs),
+        // you should assume custom_args is Some (even if no args were passed
+        // through the command line). It's None if you didn't specify any custom type.
+        let custom_args = custom_args.unwrap();
+
+        if custom_args.say_hello {
+            println!("Hello");
+        }
+
+        if let Some(population) = custom_args.starting_population {
+            for _ in 0..population {
+                context.add_person(()).unwrap();
             }
         }