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  1. #include <iostream>
  2. #include <functional>
  3.  
  4. template < typename T >
  5. class my_ {
  6.     T value;
  7.     std::function<void(T const &)> notifier;
  8.  public:
  9.     template < typename F >
  10.     my_( T const & init, F f )
  11.     : value( init ), notifier( f ) {  }
  12.     // for write
  13.     T& operator=( T const & next ) {
  14.         if( !std::equal_to<T>()(value, next) )
  15.             notifier( next );
  16.  
  17.         return value = next;
  18.     }
  19.     // for read
  20.     operator T const & () const
  21.     { return value; }
  22. }; 
  23.  
  24. struct Foo {
  25.     Foo( int init )
  26.     : value( init, 
  27.              []( int const & next ) {
  28.                  std::cout << "\tvalue changed to :" << next << std::endl; 
  29.  
  30.              } )
  31.     { }
  32.  
  33.     my_<int> value;  
  34. };
  35.  
  36. int main() {
  37.  
  38.     Foo foo( 2 );
  39.     // write
  40.     int new_values[] = { 1, 1, 1, 2, 3, 3 };
  41.     size_t const size = sizeof(new_values) / sizeof(*new_values);
  42.  
  43.     for( size_t i = 0; i != size; ++i ) {
  44.         std::cout << "set in index: " << i << std::endl;
  45.         foo.value = new_values[ i ];
  46.     }
  47.  
  48.     // read
  49.     std::cout << "final value: " << foo.value << std::endl;
  50. }
Success #stdin #stdout 0s 3032KB
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stdin
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Standard input is empty
stdout
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set in index: 0
	value changed to :1
set in index: 1
set in index: 2
set in index: 3
	value changed to :2
set in index: 4
	value changed to :3
set in index: 5
final value: 3
https://ideone.com/MZUaZG
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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