Metaprogramming

FAQ

What is metaprogramming in the context of Boost C++?

Metaprogramming is a technique of programming that involves generating and manipulating programs. In the context of Boost and C++, metaprogramming often refers to template metaprogramming, which uses templates to perform computations at compile-time.
What is Boost.MP11?

Boost.Mp11 is a Boost library designed for metaprogramming using C++11. It provides a set of templates and types for compile-time computations and manipulations, effectively extending the C++ template mechanism.
What can I achieve with Boost.MP11?

With Boost.Mp11, you can perform computations and logic at compile-time, thus reducing runtime overhead. For example, you can manipulate types, perform iterations, make decisions, and do other computations during the compilation phase.
What is a typelist and how can I use it with Boost.MP11?

A typelist is a compile-time container of types. It’s a fundamental concept in C++ template metaprogramming where operations are done at compile time rather than runtime, and types are manipulated in the same way that values are manipulated in regular programming.

In the context of the Boost.Mp11 library, a typelist is a template class that takes a variadic list of type parameters. Here’s an example:
```
#include <boost/mp11/list.hpp>

using my_typelist = boost::mp11::mp_list<int, float, double>;
```
In this example, my_typelist is a typelist containing the types int, float, and double. Once you have a typelist, you can manipulate it using the metaprogramming functions provided by the library. For example:
```
#include <boost/mp11/list.hpp>
#include <boost/mp11/algorithm.hpp>

using my_typelist = boost::mp11::mp_list<int, float, double>;

// Get the number of types in the list
constexpr std::size_t size = boost::mp11::mp_size<my_typelist>::value;

// Check if a type is in the list
constexpr bool contains_double = boost::mp11::mp_contains<my_typelist, double>::value;

// Add a type to the list
using extended_typelist = boost::mp11::mp_push_back<my_typelist, char>;

// Get the second type in the list
using second_type = boost::mp11::mp_at_c<my_typelist, 1>;
```
In these examples, mp_size is used to get the number of types in the list, mp_contains checks if a type is in the list, mp_push_back adds a type to the list, and mp_at_c retrieves a type at a specific index in the list. All these operations are done at compile time.
What are some limitations or challenges of metaprogramming with Boost.MP11?

Metaprogramming with Boost.Mp11 can lead to complex and difficult-to-understand code, especially for programmers unfamiliar with the technique. Compile errors can be particularly cryptic due to the way templates are processed. Additionally, heavy use of templates can lead to longer compile times.

Other challenges include lack of runtime flexibility, as decisions are made at compile time. And perhaps issues with portability can occur (say, between compilers) as metaprogramming pushes the boundaries of a computer language to its limits.

Boost.Mp11 supersedes the earlier Boost.Mpl and Boost.Preprocessor libraries.

Metaprogramming

FAQ

See Also