/* The following code example is taken from the book
* "C++ Templates - The Complete Guide"
* by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
*
* (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <stddef.h>
#include <cassert>
template<typename T>
class SArray {
public:
// create array with initial size
explicit SArray (size_t s)
: storage(new T[s]), storage_size(s) {
init();
}
// copy constructor
SArray (SArray<T> const& orig)
: storage(new T[orig.size()]), storage_size(orig.size()) {
copy(orig);
}
// destructor: free memory
~SArray() {
delete[] storage;
}
// assignment operator
SArray<T>& operator= (SArray<T> const& orig) {
if (&orig!=this) {
copy(orig);
}
return *this;
}
// return size
size_t size() const {
return storage_size;
}
// index operator for constants and variables
T operator[] (size_t idx) const {
return storage[idx];
}
T& operator[] (size_t idx) {
return storage[idx];
}
protected:
// init values with default constructor
void init() {
for (size_t idx = 0; idx<size(); ++idx) {
storage[idx] = T();
}
}
// copy values of another array
void copy (SArray<T> const& orig) {
assert(size()==orig.size());
for (size_t idx = 0; idx<size(); ++idx) {
storage[idx] = orig.storage[idx];
}
}
private:
T* storage; // storage of the elements
size_t storage_size; // number of elements
};
// include helper class traits template to select whether to refer to an
// ''expression template node'' either ''by value'' or ''by reference.''
/* helper traits class to select how to refer to an ''expression template node''
* - in general: by reference
* - for scalars: by value
*/
template <typename T> class A_Scalar;
// primary template
template <typename T>
class A_Traits {
public:
typedef T const& ExprRef; // type to refer to is constant reference
};
// partial specialization for scalars
template <typename T>
class A_Traits<A_Scalar<T> > {
public:
typedef A_Scalar<T> ExprRef; // type to refer to is ordinary value
};
// class for objects that represent the addition of two operands
template <typename T, typename OP1, typename OP2>
class A_Add {
private:
typename A_Traits<OP1>::ExprRef op1; // first operand
typename A_Traits<OP2>::ExprRef op2; // second operand
public:
// constructor initializes references to operands
A_Add (OP1 const& a, OP2 const& b)
: op1(a), op2(b) {
}
// compute sum when value requested
T operator[] (size_t idx) const {
return op1[idx] + op2[idx];
}
// size is maximum size
size_t size() const {
assert (op1.size()==0 || op2.size()==0
|| op1.size()==op2.size());
return op1.size()!=0 ? op1.size() : op2.size();
}
};
// class for objects that represent the multiplication of two operands
template <typename T, typename OP1, typename OP2>
class A_Mult {
private:
typename A_Traits<OP1>::ExprRef op1; // first operand
typename A_Traits<OP2>::ExprRef op2; // second operand
public:
// constructor initializes references to operands
A_Mult (OP1 const& a, OP2 const& b)
: op1(a), op2(b) {
}
// compute product when value requested
T operator[] (size_t idx) const {
return op1[idx] * op2[idx];
}
// size is maximum size
size_t size() const {
assert (op1.size()==0 || op2.size()==0
|| op1.size()==op2.size());
return op1.size()!=0 ? op1.size() : op2.size();
}
};
int main()
{
SArray<double> x(1000), y(1000);
//...
//x = 1.2*x + x*y;
}
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