whats a lambda

1add = lambda a, b : a + b
2add(3,6) ## 9

1A lambda expression is a short block 
2of code which takes in parameters
3and returns a value. Lambda expressions
4are similar to methods, but they do
5not need a name and they can be
6implemented right in the body of a method.
7
8parameter -> expression
9
10To use more than one parameter, wrap them in parentheses:
11
12(parameter1, parameter2) -> expression
13
14Example
15Use a lamba expression in the ArrayList's 
16forEach() method to print every item in the list:
17
18import java.util.ArrayList;
19
20public class Main {
21  public static void main(String[] args) {
22    ArrayList<Integer> numbers = new ArrayList<Integer>();
23    numbers.add(5);
24    numbers.add(9);
25    numbers.add(8);
26    numbers.add(1);
27    numbers.forEach( (n) -> { System.out.println(n); } );
28  }
29}
30

1// C++ program to demonstrate lambda expression in C++
2#include <bits/stdc++.h>
3using namespace std;
4  
5// Function to print vector
6void printVector(vector<int> v)
7{
8    // lambda expression to print vector
9    for_each(v.begin(), v.end(), [](int i)
10    {
11        std::cout << i << " ";
12    });
13    cout << endl;
14}
15  
16int main()
17{
18    vector<int> v {4, 1, 3, 5, 2, 3, 1, 7};
19  
20    printVector(v);
21  
22    // below snippet find first number greater than 4
23    // find_if searches for an element for which
24    // function(third argument) returns true
25    vector<int>:: iterator p = find_if(v.begin(), v.end(), [](int i)
26    {
27        return i > 4;
28    });
29    cout << "First number greater than 4 is : " << *p << endl;
30  
31  
32    // function to sort vector, lambda expression is for sorting in
33    // non-decreasing order Compiler can make out return type as
34    // bool, but shown here just for explanation
35    sort(v.begin(), v.end(), [](const int& a, const int& b) -> bool
36    {
37        return a > b;
38    });
39  
40    printVector(v);
41  
42    // function to count numbers greater than or equal to 5
43    int count_5 = count_if(v.begin(), v.end(), [](int a)
44    {
45        return (a >= 5);
46    });
47    cout << "The number of elements greater than or equal to 5 is : "
48         << count_5 << endl;
49  
50    // function for removing duplicate element (after sorting all
51    // duplicate comes together)
52    p = unique(v.begin(), v.end(), [](int a, int b)
53    {
54        return a == b;
55    });
56  
57    // resizing vector to make size equal to total different number
58    v.resize(distance(v.begin(), p));
59    printVector(v);
60  
61    // accumulate function accumulate the container on the basis of
62    // function provided as third argument
63    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
64    int f = accumulate(arr, arr + 10, 1, [](int i, int j)
65    {
66        return i * j;
67    });
68  
69    cout << "Factorial of 10 is : " << f << endl;
70  
71    //     We can also access function by storing this into variable
72    auto square = [](int i)
73    {
74        return i * i;
75    };
76  
77    cout << "Square of 5 is : " << square(5) << endl;
78}

1x = lambda a, b, c, d, e, f: a + b + c + d + e + f
2print(x(31231, 312, 312, 31, 12, 31))