Can lambda functions be templated?

In C++, lambda expressions themselves cannot be directly templated because they are anonymous and lack names, so you cannot template them in the same way as you would for ordinary functions or classes. However, you can indirectly achieve similar functionality through several approaches:

1. Parameters with Automatic Type Deduction

Lambda expressions can utilize the auto keyword for automatic type deduction, which can achieve effects similar to template functions in many cases. For example:

cpp
auto myLambda = [](auto x, auto y) {
    return x + y;
};

std::cout << myLambda(5, 3) << std::endl;  // Output: 8
std::cout << myLambda(2.5, 3.0) << std::endl;  // Output: 5.5

In this example, myLambda can accept parameters of any type, behaving similarly to a function using templates.

2. Encapsulating within Template Functions

Another approach is to encapsulate the lambda expression within a template function. This allows you to define the lambda inside a function template and instantiate it as needed. For example:

cpp
template<typename T>
void process(T x, T y) {
    auto lambda = [](T a, T b) {
        return a + b;
    };
    std::cout << lambda(x, y) << std::endl;
}

process(10, 20);  // Output: 30
process(1.1, 2.2);  // Output: 3.3

3. Using Generic Lambdas (C++14 and later)

Starting from C++14, lambda expressions support generic programming, where auto is used as the parameter type. This allows lambdas to handle inputs of different types flexibly, as shown in the first example.

Summary

Although lambda expressions cannot be directly templated, using generic lambdas or encapsulating them within template functions can achieve similar flexibility and generality to templated functions. These techniques are very useful when working with different types.