[LLVMdev] Small dyn_cast embellishment

[Vladimir Prus]

It appears that LLVM has quite a number of dyn_casts (which I find quite 
natural) The suggested idiom:

   if (ConstantExpr* ce = dyn_cast<ConstantExpr>(*j)) {
	
   }

is fine, and IIRC even used in TC++PL, but it occured to me that we can do 
even better:

   if (dyn_caster<ConstantExpr> ce = *j) {
   }

where dyn_caster is defined like this:

    template<class T>
    class dyn_caster
    {
    public:
        template<class T2>
        dyn_caster(T2& t)
        : m_ptr(dyn_cast<T>(t))
        {}

        T& operator*() const { return *m_ptr; }
        T* operator->() const { return m_ptr; }
        operator void*() const { return m_ptr; }
    private:
        T* m_ptr;
    };

This allows to type the type name only once, not twice. I'm not sure if this 
good idea yet, but though I'd just throw it in, in case anybody will be 
interested.

- Volodya