formatting helper to join a collection into a string

Ouch!
Why does C++ lack the most basic everyday stuff?
It needn't be performant. It needn't support some fancy
higher order container. Just join the f***ing strings.

use Bosst??  -- OMG!! pulls in half the metra programming library
and tries to work on any concievable range like object. Just
somehow our Lumiera Forward Iterators aren't "range-like" enough
for boost's taste.

Thus let's code up that fucking for-loop ourselves, once and forever.

src/lib/format-util.hpp

@@ -38,10 +38,12 @@
 #define LIB_FORMAT_UTIL_H
 
 #include "lib/meta/trait.hpp"
+#include "lib/itertools.hpp"
 #include "lib/symbol.hpp"
 #include "lib/util.hpp"
 
 #include <string>
+#include <sstream>
 #include <cstring>
 #include <typeinfo>
 #include <boost/lexical_cast.hpp>
@@ -59,6 +61,7 @@ namespace util {
   using boost::enable_if;
   using lib::meta::can_ToString;
   using lib::meta::can_lexical2string;
+  using lib::meta::can_IterForEach;
   using lib::Symbol;
   using util::isnil;
   using std::string;
@@ -143,5 +146,67 @@ namespace util {
                      : tyStr(val);
   }
   
+  namespace { // helper to build range iterator on demand
+    template<class CON, typename TOGGLE = void>
+    struct _RangeIter
+      {
+        using StlIter = typename CON::const_iterator;
+        
+        lib::RangeIter<StlIter> iter;
+        
+        _RangeIter(CON const& collection)
+          : iter(begin(collection), end(collection))
+          { }
+      };
+    
+    template<class IT>
+    struct _RangeIter<IT,   typename enable_if< can_IterForEach<IT> >::type>
+      {
+        IT iter;
+        
+        _RangeIter(IT&& srcIter)
+          : iter(std::forward<IT>(srcIter))
+          { }
+        
+      };
+  }
+  
+  /**
+   * enumerate a collection's contents, separated by delimiter.
+   * @param coll something that is standard-iterable
+   * @return all contents converted to string and joined into
+   *         a single string, with separators interspersed.
+   * @remarks based on the \c boost::join library function,
+   *          which in turn is based on
+   *          additionally, we use our
+   *          \link #str failsafe string conversion \endlink
+   *          which in turn invokes custom string conversion,
+   *          or lexical_cast as appropriate.
+   */
+  template<class CON>
+  inline string
+  join (CON&& coll, string const& delim =", ")
+  {
+    using Coll = typename lib::meta::Strip<CON>::Type;
+    using Val =  typename Coll::value_type;
+    
+    std::function<string(Val const&)> toString = [] (Val const& val) { return str(val); };
+    
+    _RangeIter<Coll> range(std::forward<Coll>(coll));
+    auto strings = lib::transformIterator(range.iter, toString);
+    
+    if (!strings) return "";
+    
+    std::ostringstream buffer;
+    for (string const& elm : strings)
+        buffer << elm << delim;
+    
+    // chop off last delimiter
+    size_t len = buffer.str().length();
+    ASSERT (len > delim.length());
+    return buffer.str().substr(0, len - delim.length());
+  }
+  
+  
 } // namespace util
 #endif

src/proc/control/memento-tie.hpp

@@ -45,7 +45,6 @@
 #include "lib/meta/function-closure.hpp"
 #include "proc/control/command-signature.hpp"
 #include "lib/functor-util.hpp"
-#include "lib/format-util.hpp"
 #include "lib/util.hpp"
 
 #include <boost/operators.hpp>
@@ -181,19 +180,8 @@ namespace control {
           return undo_ && capture_ && isCaptured_;
         }
       
-      
-      operator std::string()  const
-        {
-          if (!undo_ || !capture_)
-            return "·noUNDO·";
-          
-          if (!isCaptured_)
-            return "<mem:missing>";
-          
-          return "<" 
-               + util::str(memento_, "mem: ", "·memento·") 
-               + ">";
-        }
+      /** for diagnostics: include format-util.hpp */
+      operator std::string()  const;
       
       
       /// Supporting equality comparisons...
@@ -212,6 +200,24 @@ namespace control {
     };
   
 
+  template<typename SIG, typename MEM>
+  MementoTie<SIG,MEM>::operator std::string()  const
+  {
+    if (!undo_ || !capture_)
+      return "·noUNDO·";
+    
+    if (!isCaptured_)
+      return "<mem:missing>";
+    
+    return "<"
+#ifdef LIB_FORMAT_UTIL_H
+         + util::str(memento_, "mem: ", "·memento·")
+#else
+         + std::string("memento")
+#endif
+         + ">";
+  }
+  
   
   
 }} // namespace proc::control

tests/15library.tests

@@ -187,6 +187,8 @@ out: ^he says: hey Joe!
 out: ^the truth: 0
 out: ^just a number: 1.234.*e\+56
 out: ^12345X
+out: 0.+1.1.+2.2.+3.3.+4.4.+5.5.+6.6.+7.7.+8.8.+\-\-\+\-\-9.9
+out-lit: Nr.01(0.0), Nr.02(2.2), Nr.03(4.4), Nr.04(6.6), Nr.05(8.8), Nr.06(11.0), Nr.07(13.2), Nr.08(15.4), Nr.09(17.6), Nr.10(19.8)
 return: 0
 END
 

tests/library/format-helper-test.cpp

@@ -23,10 +23,22 @@
 
 #include "lib/test/run.hpp"
 #include "lib/format-util.hpp"
+#include "lib/format-string.hpp"
+#include "lib/iter-adapter-stl.hpp"
 #include "lib/error.hpp"
 
 #include <iostream>
+#include <vector>
+#include <string>
 
+
+using lib::transformIterator;
+using lib::iter_stl::eachElm;
+using util::_Fmt;
+
+using std::vector;
+using std::string;
+using std::to_string;
 using std::cout;
 using std::endl;
 
@@ -46,22 +58,46 @@ namespace test {
   
   
   
+  class AutoCounter
+    {
+      static uint cnt;
+      
+      uint id_;
+      double d_;
+      
+    public:
+      AutoCounter(double d)
+        : id_(++cnt)
+        , d_(d*2)
+        { }
+      
+      operator string()  const
+        {
+          return _Fmt("Nr.%02d(%3.1f)") % id_ % d_;
+        }
+    };
+  uint AutoCounter::cnt = 0;
+  
+  
+  
   /***************************************************************************//**
    * @test verifies the proper working of some string-formatting helper functions.
    *       - util::str() provides a failsafe to-String conversion, preferring
    *         an built-in conversion, falling back to just a mangled type string.
    * @see format-util.hpp
    */
-  class FormatHelper_test : public Test
+  class FormatHelper_test
+    : public Test
     {
       void
       run (Arg)
         {
           check2String();
+          checkStringJoin();
         }
       
       
-      /** @test verify a failasfe to-string conversion. */
+      /** @test verify a failsafe to-string conversion. */
       void
       check2String ()
         {
@@ -82,7 +118,30 @@ namespace test {
         }
       
       
+      /** @test verify delimiter separated joining of arbitrary collections.
+       *        - the first test uses a STL container, which means we need to wrap
+       *          into a lib::RangeIter. Moreover, lexical_cast is used to convert
+       *          the double numbers into strings.
+       *        - the second test uses an inline transforming iterator to build a
+       *          series of AutoCounter objects, which provide a custom string
+       *          conversion function. Moreover, since the transforming iterator
+       *          conforms to the Lumiera Forward Iterator concept, we can just
+       *          move the rvalue into the formatting function without much ado
+       */
+      void
+      checkStringJoin()
+        {
+          vector<double> dubious;
+          for (uint i=0; i<10; ++i)
+            dubious.push_back(1.1*i);
           
+          std::function<AutoCounter(double)> justCount = [](double d){ return AutoCounter(d); };
+          
+          
+          cout << join(dubious, "--+--") << endl;
+          cout << join(transformIterator(eachElm(dubious)
+                                        ,justCount)) << endl;
+        }
     };
   
   LAUNCHER (FormatHelper_test, "unit common");