Lambda expression
` `[ capture ]( parameters ) -> return_type { function_body }

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* An example lambda function is defined as follows:
*

` `[]( int x , int y ) -> int { return x + y ; }

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* C++11 also supports closures. Closures are defined between square brackets `[` and `]` in the declaration of lambda expression.
* The mechanism allows these variables to be captured by value or by reference. The following table demonstrates this:

```
```[] //no variables defined. Attempting to use any external variables in the lambda is an error.
[ x , & y ] //x is captured by value, y is captured by reference
[ & ] //any external variable is implicitly captured by reference if used
[ = ] //any external variable is implicitly captured by value if used
[ & , x ] //x is explicitly captured by value. Other variables will be captured by reference
[ = , & z ] // z is explicitly captured by reference . Other variables will be captured by value

#include <iostream>
#include <vector>
#include <algorithm>
void c11_lambda ()
{
std :: vector < int > some_list { 1 , 2 , 3 , 4 , 5 };
std :: for_each ( some_list . begin (), some_list . end (), []( int x ) { std :: cout << x << std :: endl ;});
int sum_1 ( 0 );
int sum_2 ( 0 );
// error: 'sum_1' is not captured
// error: 'sum_2' is not captured
// std::for_each(some_list.begin(), some_list.end(), [](int x){sum_1 += x; sum_2 += x;});
std :: for_each ( some_list . begin (), some_list . end (), [ & ]( int x ) { sum_1 += x ; sum_2 += x ;});
std :: cout << "sum_1 = " << sum_1 << " sum_2 = " << sum_2 << std :: endl ;
// error: assignment of read-only variable 'sum_1'
// std::for_each(some_list.begin(), some_list.end(), [=](int x){sum_1 += x; sum_2 += x;});
sum_1 = sum_2 = 0 ;
// error: assignment of read-only variable 'sum_2'
// std::for_each(some_list.begin(), some_list.end(), [&, sum_2](int x){sum_1 += x; sum_2 += x;});
std :: for_each ( some_list . begin (), some_list . end (), [ & , sum_2 ]( int x ) { sum_1 += x ;});
std :: cout << "sum_1 = " << sum_1 << " sum_2 = " << sum_2 << std :: endl ;
sum_1 = sum_2 = 0 ;
// error: assignment of read-only variable 'sum_1'
// std::for_each(some_list.begin(), some_list.end(), [=, &sum_2](int x){sum_1 += x; sum_2 += x;});
std :: for_each ( some_list . begin (), some_list . end (), [ = , & sum_2 ]( int x ){ sum_2 += x ;});
std :: cout << "sum_1 = " << sum_1 << " sum_2 = " << sum_2 << std :: endl ;
}

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sum_1 = 15 sum_2 = 15
sum_1 = 15 sum_2 = 0
sum_1 = 0 sum_2 = 15