From 5be35a407fdb363d95ef9bbfe0e87c35c1de7777 Mon Sep 17 00:00:00 2001
From: Ichthyostega <prg@ichthyostega.de>
Date: Tue, 5 Jan 2016 23:52:48 +0100
Subject: [PATCH] toString(#985): new minimal string-conversion facility

now placed into the very basic header lib/meta/util.hpp
---
 research/try.cpp      | 21 ++-------------------
 src/lib/meta/util.hpp | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 19 deletions(-)

diff --git a/research/try.cpp b/research/try.cpp
index 78be072e2..643d3a728 100644
--- a/research/try.cpp
+++ b/research/try.cpp
@@ -58,7 +58,7 @@
  ** between values, references and pointers, which also means, we do
  ** not want to indicate pointers explicitly (just signal NULL, when
  ** encountered). The situation is slightly different for the `ostream`
- ** inserter; in a moder GUI application, there isn't much use for
+ ** inserter; in a modern GUI application, there isn't much use for
  ** STDOUT and STDERR, beyond error messages and unit testing.
  ** Thus, we can strive at building a more convenient flavour
  ** here, which does indeed even shows the address of pointers.
@@ -83,6 +83,7 @@ using lib::P;
 using lib::meta::enable_if;
 using lib::meta::typeStr;
 using lib::meta::can_convertToString;
+using lib::meta::CustomStringConv;
 
 using std::string;
 using std::cout;
@@ -94,24 +95,6 @@ using std::endl;
 
 
 
-///////////////////////////////planned minimal conversion, maybe in meta/util.hpp ?
-  template<typename X, typename COND =void>
-  struct CustomStringConv
-    {
-      static string invoke (X const& x) { return "«"+typeStr(x)+"»"; }
-    };
-  
-  template<typename X>
-  struct CustomStringConv<X,     enable_if<can_convertToString<X>> >
-    {
-      static string
-      invoke (X const& val)
-        try        { return string(val); }
-        catch(...) { return "↯"; }
-    };
-///////////////////////////////planned minimal conversion, maybe in meta/util.hpp ?
-
-
 ///////////////////////////////shall go into the implementation of lib::P
 template<typename X>
 inline string
diff --git a/src/lib/meta/util.hpp b/src/lib/meta/util.hpp
index 2ac910290..b519cff39 100644
--- a/src/lib/meta/util.hpp
+++ b/src/lib/meta/util.hpp
@@ -220,5 +220,34 @@ namespace meta {
   
   
   
+  /** failsafe invocation of custom string conversion.
+   * @return string to represent the object, by default a [type display](\ref typeStr)
+   * @remarks this is a lightweight solution to at least _get any human readable string
+   *    representation for pretty much every language object._ This minimal solution
+   *    is defined here, to allow for built-in diagnostics for custom types without
+   *    the danger of creating much header inclusion and code size bloat. A more
+   *    elaborate, [extended solution](lib::toString), including _lexical conversions
+   *    for numbers,_ is defined in format-obj.hpp
+   * @note any exceptions during string conversion are caught and silently ignored;
+   *    the returned string indicates "↯" in this case.
+   */
+  template<typename X, typename COND =void>
+  struct CustomStringConv
+    {
+      static std::string invoke (X const& x) { return "«"+typeStr(x)+"»"; }
+    };
+  
+  template<typename X>
+  struct CustomStringConv<X,     enable_if<can_convertToString<X>> >
+    {
+      static std::string
+      invoke (X const& val)
+        try        { return std::string(val); }
+        catch(...) { return "↯"; }
+    };
+
+  
+  
+  
 }} // namespace lib::meta
 #endif