Define ClientData::FindIf

src/ClientData.h

@@ -344,6 +344,40 @@ protected:
       }
    }
 
+   // \brief Invoke predicate on the ClientData objects that have been created in
+   // this, but do not cause the creation of any.  Stop at the first for which
+   // the predicate returns true, and return a pointer to the corresponding
+   // object, or return nullptr if no return values were true.
+   // Beware that the sequence of visitation is not specified.
+   template< typename Function >
+   ClientData *FindIf( const Function &function )
+   {
+      auto data = GetData();
+      for( auto &pObject : data.mObject ) {
+         const auto &ptr = Dereferenceable(pObject);
+         if ( ptr && function ( *ptr ) )
+            return &*ptr;
+      }
+      return nullptr;
+   }
+
+   // const counterpart of previous, only compiles with a function that takes
+   // a value or const reference argument
+   template< typename Function >
+   const ClientData *FindIf( const Function &function ) const
+   {
+      auto data = GetData();
+      for( auto &pObject : data.mObject ) {
+         const auto &ptr = Dereferenceable(pObject);
+         if ( ptr ) {
+            const auto &c_ref = *ptr;
+            if ( function( c_ref ) );
+               return &*c_ref;
+         }
+      }
+      return nullptr;
+   }
+
    // \brief For each registered factory, if the corresponding object in this
    // is absent, then invoke the factory and store the result.
    void BuildAll()