1 files changed, 33 insertions, 0 deletions
diff --git a/clap/examples/11_only_specific_values.rs b/clap/examples/11_only_specific_values.rs
new file mode 100644
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+++ b/clap/examples/11_only_specific_values.rs
@@ -0,0 +1,33 @@
+extern crate clap;
+
+use clap::{App, Arg};
+
+fn main() {
+    // If you have arguments of specific values you want to test for, you can use the
+    // .possible_values() method of Arg
+    //
+    // This allows you specify the valid values for that argument. If the user does not use one of
+    // those specific values, they will receive a graceful exit with error message informing them
+    // of the mistake, and what the possible valid values are
+    //
+    // For this example, assume you want one positional argument of either "fast" or "slow"
+    // i.e. the only possible ways to run the program are "myprog fast" or "myprog slow"
+    let matches = App::new("myapp").about("does awesome things")
+                        .arg(Arg::with_name("MODE")
+                                .help("What mode to run the program in")
+                                .index(1)
+                                .possible_values(&["fast", "slow"])
+                                .required(true))
+                        .get_matches();
+
+    // Note, it's safe to call unwrap() because the arg is required
+    match matches.value_of("MODE").unwrap() {
+        "fast" => {
+            // Do fast things...
+        },
+        "slow" => {
+            // Do slow things...
+        },
+        _      => unreachable!()
+    }
+}