From 6a1389bbe1dff71bba033f88c3c0eb039895efcf Mon Sep 17 00:00:00 2001
From: Eirik Tsarpalis <eirik.tsarpalis@gmail.com>
Date: Wed, 29 Jun 2016 13:39:02 +0300
Subject: [PATCH] implement ExactlyOnceAttribute

---
 src/Argu/PreCompute.fs | 5 +++--
 src/Argu/Types.fs      | 5 +++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/Argu/PreCompute.fs b/src/Argu/PreCompute.fs
index b0f033c2..42e1a2ec 100644
--- a/src/Argu/PreCompute.fs
+++ b/src/Argu/PreCompute.fs
@@ -139,8 +139,9 @@ let rec private preComputeUnionCaseArgInfo (stack : Type list) (helpParam : Help
 
     let isFirst = uci.ContainsAttribute<FirstAttribute> ()
     let isAppSettingsCSV = uci.ContainsAttribute<ParseCSVAttribute> ()
-    let isMandatory = uci.ContainsAttribute<MandatoryAttribute> (true)
-    let isUnique = uci.ContainsAttribute<UniqueAttribute> (true)
+    let isExactlyOnce = uci.ContainsAttribute<ExactlyOnceAttribute>(true)
+    let isMandatory = isExactlyOnce || uci.ContainsAttribute<MandatoryAttribute> (true)
+    let isUnique = isExactlyOnce || uci.ContainsAttribute<UniqueAttribute> (true)
     let isGatherAll = uci.ContainsAttribute<GatherAllSourcesAttribute> ()
     let isRest = uci.ContainsAttribute<RestAttribute> ()
     let isHidden = uci.ContainsAttribute<HiddenAttribute> ()
diff --git a/src/Argu/Types.fs b/src/Argu/Types.fs
index facf5d92..5b376fe9 100644
--- a/src/Argu/Types.fs
+++ b/src/Argu/Types.fs
@@ -30,6 +30,11 @@ module ArguAttributes =
     [<AttributeUsage(AttributeTargets.Class ||| AttributeTargets.Property, AllowMultiple = false)>]
     type UniqueAttribute () = inherit Attribute ()
 
+    /// Demands that the argument should be specified exactly once; an exception is raised otherwise.
+    /// Equivalent to attaching both the Mandatory and Unique attribute on the parameter.
+    [<AttributeUsage(AttributeTargets.Class ||| AttributeTargets.Property, AllowMultiple = false)>]
+    type ExactlyOnceAttribute () = inherit Attribute ()
+
     /// Gathers all parsed results from both AppSettings and command line.
     [<AttributeUsage(AttributeTargets.Class ||| AttributeTargets.Property, AllowMultiple = false)>]
     type GatherAllSourcesAttribute () = inherit Attribute ()