From 35dd24f46f3335b8f152bcf20e86b30eb5ee49b4 Mon Sep 17 00:00:00 2001
From: Michael Davidsaver <mdavidsaver@gmail.com>
Date: Wed, 18 Dec 2019 18:25:11 -0800
Subject: [PATCH] Value::tryAs() tryFrom()

---
 src/data.cpp    | 24 ++++++++++++++++++++++++
 src/pvxs/data.h | 33 +++++++++++++++++++--------------
 2 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/src/data.cpp b/src/data.cpp
index c6704b1..4c7fb67 100644
--- a/src/data.cpp
+++ b/src/data.cpp
@@ -241,6 +241,18 @@ void Value::copyOut(void *ptr, StoreType type) const
     throw NoConvert();
 }
 
+bool Value::tryCopyOut(void *ptr, StoreType type) const
+{
+    try {
+        copyOut(ptr, type);
+        return true;
+    }catch(NoField&){
+        return false;
+    }catch(NoConvert&){
+        return false;
+    }
+}
+
 namespace {
 // C-style cast between scalar storage types, and print to string (base 10)
 template<typename Dest>
@@ -342,6 +354,18 @@ void Value::copyIn(const void *ptr, StoreType type)
     mark();
 }
 
+bool Value::tryCopyIn(const void *ptr, StoreType type)
+{
+    try {
+        copyIn(ptr, type);
+        return true;
+    }catch(NoField&){
+        return false;
+    }catch(NoConvert&){
+        return false;
+    }
+}
+
 void Value::traverse(const std::string &expr, bool modify)
 {
     size_t pos=0;
diff --git a/src/pvxs/data.h b/src/pvxs/data.h
index db4ae65..5d6c747 100644
--- a/src/pvxs/data.h
+++ b/src/pvxs/data.h
@@ -286,14 +286,16 @@ public:
 
     // use with caution
     void copyOut(void *ptr, StoreType type) const;
-    //bool tryCopyOut(void *ptr, impl::StoreType type) const;
+    bool tryCopyOut(void *ptr, StoreType type) const;
     void copyIn(const void *ptr, StoreType type);
-    //bool tryCopyIn(const void *ptr, impl::StoreType type);
+    bool tryCopyIn(const void *ptr, StoreType type);
 
-//    template<typename T>
-//    inline bool tryAs(T& val) const {
-//        return tryCopyOut(&val, std::type_index(typeid(std::decay<T>::type)));
-//    }
+    template<typename T>
+    inline bool tryAs(T& val) const {
+        typedef impl::StorageMap<typename std::decay<T>::type> map_t;
+        typename map_t::store_t ret;
+        return tryCopyOut(&ret, map_t::code);
+    }
 
     /** Extract value from field.
      */
@@ -304,15 +306,18 @@ public:
         copyOut(&ret, map_t::code);
         return ret;
     }
-//    template<typename T>
-//    void as(T& val) const {
-//        copyOut(&val, std::type_index(typeid(typename std::decay<T>::type)));
-//    }
 
-//    template<typename T>
-//    inline bool tryFrom(const T& val) {
-//        return tryCopyIn(&val, std::type_index(typeid(std::decay<T>::type)));
-//    }
+    template<typename T>
+    inline void as(T& val) const {
+        val = this->as<T>();
+    }
+
+    template<typename T>
+    inline bool tryFrom(const T& val) {
+        typedef impl::StorageMap<typename std::decay<T>::type> map_t;
+        typename map_t::store_t norm(val);
+        return copyIn(&norm, map_t::code);
+    }
 
     template<typename T>
     void from(const T& val) {