Lambda Expression

INFO

The predicate, anonymous, inline function that can be defined directly in the code without giving it a name → One time use

Syntax

[capture](parameters) -> return_type {
	// function body
}

• [] Capture Clause: lets the lambda access variables from the surrounding scope
  • [=]: Captures all external variables by value
  • [&]: Capture all external variables by reference
  • [a, &b]: Capture a by value, b by reference
  • []: No capture, only using local variables
• (parameters) Parameter List: like any function’s arguments
• -> return_type Return Type: Optional since compiler usually infers the return type
• {...} Function Body: the logic to execute;

Example

Using std::for_each function

vector<int> v = {10, 25, 67, 26, 21, 10};
int sum = 0;
for_each(v.begin(), v.end(), [&sum](const auto& elements){sum += element;})
cout << sum << endl;

• [&sum] → captures sum variable by reference (since need to update it)
• (const auto& element) → captures each element in vector v
• {sum += element;} → Execute this code for every element in vector v