From aa1f893dbe2f48c7a643c15db35802440664f60b Mon Sep 17 00:00:00 2001
From: Robin Krahl <robin.krahl@ireas.org>
Date: Tue, 7 Jan 2020 13:07:15 +0000
Subject: Implement Default in the Enum! and Command! macros

For the transition to structopt, we have to be able to easily construct
enum variants once we have added fields to them.  Therefore we implement
the Default trait in the generated macros by choosing the first variant
as the default.
---
 nitrocli/src/arg_util.rs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/nitrocli/src/arg_util.rs b/nitrocli/src/arg_util.rs
index b98aa34..075dc6d 100644
--- a/nitrocli/src/arg_util.rs
+++ b/nitrocli/src/arg_util.rs
@@ -76,6 +76,8 @@ macro_rules! Command {
         }
       }
     }
+
+    impl_default!($name => $( $name::$var(::std::default::Default::default()) , )*);
   };
   ( $name:ident, [ $( $var:ident => ($str:expr, $exec:expr), ) *] ) => {
     #[derive(Debug, PartialEq)]
@@ -128,6 +130,8 @@ macro_rules! Command {
         }
       }
     }
+
+    impl_default!($name => $( $name::$var , )*);
   };
 }
 
@@ -204,6 +208,19 @@ macro_rules! enum_int {
         }
       }
     }
+
+    impl_default!($name => $( $name::$var , )*);
+
+  };
+}
+
+macro_rules! impl_default {
+  ( $name:ident => $def:expr , $( $other:expr , ) *) => {
+    impl ::std::default::Default for $name {
+      fn default() -> Self {
+        $def
+      }
+    }
   };
 }
 
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