From 403b2edb62e0ccc868cd29bb806a22d0835ce2c3 Mon Sep 17 00:00:00 2001
From: Michael Uleysky <uleysky@poi.dvo.ru>
Date: Sun, 11 Oct 2015 17:33:07 +1000
Subject: [PATCH] Add function Exist() to temaplates OBType and OBTypeM to
 check if ObjectBase* pointer is non-zero.

---
 include/common.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/common.h b/include/common.h
index 9b88488..af08cac 100644
--- a/include/common.h
+++ b/include/common.h
@@ -47,30 +47,34 @@ public:
 
 
 // Template for checking and using ObjectBase derivative classes
+// Checking if arg is non-zero: if(OBType<Derived>(arg).Exist())
 // Checking if arg is pointer on Derived: if(OBType<Derived>(arg))
 // Using const ObjectBase* arg as const Derived*: OBType<Derived>(arg)->SomeCall()
 template<class O>
 class OBType
 {
  const O* p;
+ bool iszero;
  public:
  OBType() = delete;
  OBType(OBType&&) = delete;
  OBType(OBType&) = delete;
- OBType(const ObjectBase* arg) {if(0==arg) p=0; else if(typeid(*arg)==typeid(O)) p=dynamic_cast<const O*>(arg); else p=0;}
+ OBType(const ObjectBase* arg):iszero(0==p) {if(0==arg) p=0; else if(typeid(*arg)==typeid(O)) p=dynamic_cast<const O*>(arg); else p=0;}
  const O* operator->() const {return p;}
  operator bool() const {return 0!=p;}
  operator const O*() const {return p;}
+ bool Exist() const {return !iszero;}
 };
 
 
 // Template for checking and using several ObjectBase derivative classes
 // Func is template of class-function template argument of which can be any of Derived classes.
 // It must have at least one argument - pointer to constant object of Derived class and return non-void.
-// Checking if arg is pointer on any of Derived classes: if(OBType<Func,Derived>(arg))
+// Checking if arg is non-zero: if(OBTypeM<Func,Derived...>(arg).Exist())
+// Checking if arg is pointer on any of Derived classes (always false if arg is zero): if(OBTypeM<Func,Derived...>(arg))
 // Applying Func can be done by two ways:
 // 1) Function bool Apply(Res& res, args...). Here res is result of calling Func with arguments args. Result of Func is statically casted to type Res.
-// If arg is not a pointer on any of Derived classes, Apply() return false and res is not changed.
+// If arg is zero or not a pointer on any of Derived classes, Apply() return false and res is not changed.
 // 2) Overloaded operator ()(args). It returns result of calling Func with arguments args. Type of returning value is type of Func<Derived1>().
 // Full definition. Never instantiated.
 template<template<typename> class Func, class... O>
@@ -110,6 +114,7 @@ class OBTypeM<Func,O1,O...>: public OBTypeM<Func,O...>
   if(right) return Func<O1>()(dynamic_cast<const O1*>(OBTypeM<Func,O...>::P()),args...);
   else return OBTypeM<Func,O...>::template F<T,Args...>(args...);
  }
+ bool Exist() const {return OBTypeM<Func,O...>::Exist();}
 };
 
 // Partial instantiation of the bottom of recursion
@@ -130,6 +135,7 @@ class OBTypeM<Func>
  void operator ()(Args... args) const {}
  template<class Res, class... Args>
  Res F(Args... args) const {return Res();}
+ bool Exist() const {return 0!=p;}
 };