Before the advent of C++11 and subsequent standards, advanced C++ developers had to innovate to write modern, maintainable, and efficient code. Here are some examples of how they proceeded with features that were later standardized:
1- shared_ptr
Smart pointers in C++ have been used for a long time, often through custom implementations or libraries like Boost. For many C++ developers, the introduction of shared_ptr and other smart pointers in the standard library was simply a way to standardize the tools they had already been using.
#include <boost/shared_ptr.hpp> boost::shared_ptr<int> p(new int(10));
2- Range based loop:
BOOST_FOREACH is a macro provided by the Boost library in C++ to simplify iterating over containers. It predates the range-based for loop introduced in C++11 and offers a way to write cleaner and more readable code.
#include <boost/foreach.hpp>
#include <vector>
#include <iostream>
int main() {
std::vector<int> vec = {1, 2, 3, 4, 5};
BOOST_FOREACH(int& x, vec) {
std::cout << x << " ";
}
return 0;
}3- C++ Concepts
Before concepts, enable_if from <type_traits> was used to conditionally enable function templates and class specializations based on traits. It is more verbose and harder to read, often leading to complex syntax.
template <typename T>
std::enable_if_t<std::is_integral_v<T>, T> add(T a, T b) {
return a + b;
}4- Lambda Expressions:
The Boost Lambda library allows the creation of small unnamed function objects (lambdas) in C++ that can be used inline where a function object or functor is required. This is particularly useful for short operations and makes code more concise and readable.
#include <boost/lambda/lambda.hpp>
#include <iostream>
#include <algorithm>
#include <vector>
int main() {
using namespace boost::lambda;
std::vector<int> vec = {1, 2, 3, 4, 5};
std::for_each(vec.begin(), vec.end(), std::cout << (_1 * 2) << " ");
return 0;
}This code prints each element of the vector multiplied by 2.
5- constexpr
Before constexpr was introduced in C++11, developers often relied on Boost to achieve similar compile-time constant evaluation. The Boost library offers several utilities and techniques that can help mimic the behavior of constexpr.
Although not a direct replacement, BOOST_STATIC_ASSERT can be used to enforce compile-time assertions, ensuring that certain conditions are met during compilation.
Example:
#include <boost/static_assert.hpp> BOOST_STATIC_ASSERT(sizeof(int) == 4);
Boost.MPL provides also tools for compile-time computations, which can be used to achieve behavior similar to constexpr for template metaprogramming.
Example:
#include <boost/mpl/int.hpp> #include <boost/mpl/plus.hpp> #include <boost/mpl/equal_to.hpp> #include <boost/static_assert.hpp> namespace mpl = boost::mpl; typedef mpl::int_<3> three; typedef mpl::int_<4> four; typedef mpl::plus<three, four>::type seven; BOOST_STATIC_ASSERT((mpl::equal_to<seven, mpl::int_<7>>::value));
And finally Boost.Hana is a modern metaprogramming library that provides more powerful and flexible compile-time capabilities, similar to constexpr.
Example:
#include <boost/hana.hpp>
#include <iostream>
namespace hana = boost::hana;
constexpr auto sum = hana::int_c<3> + hana::int_c<4>;
int main() {
std::cout << sum << std::endl; // Outputs: 7
return 0;
}6- Type Traits
C++11: std::is_same, std::enable_if, etc.
Boost: boost::is_same, boost::enable_if, etc.
- Boost provided type traits and SFINAE utilities for template metaprogramming.
Example:
#include <boost/type_traits.hpp> boost::is_same<int, int>::value; // true
7- Static Assertions
C++11: static_assert
Boost: BOOST_STATIC_ASSERT
- Boost allowed compile-time assertions to catch errors early.
Example:
#include <boost/static_assert.hpp> BOOST_STATIC_ASSERT(sizeof(int) == 4);
8- Regular Expressions
C++11: std::regex
Boost: boost::regex
- Boost provided a powerful regular expression library.
Example:
#include <boost/regex.hpp>
boost::regex re("^[0-9]+$");9- Tuples
C++11: std::tuple
Boost: boost::tuple
- Boost provided a way to return multiple values from a function.
Example:
#include <boost/tuple/tuple.hpp> boost::tuple<int, std::string> t(1, "example");
10- Chrono
C++11: std::chrono
Boost: boost::chrono
- Boost provided utilities for time duration and clocks.
Example:
#include <boost/chrono.hpp> boost::chrono::steady_clock::time_point start = boost::chrono::steady_clock::now();
11- Threading
C++11: std::thread
Boost: boost::thread
- Boost provided threading capabilities before it was standardized.
Example:
#include <boost/thread.hpp>
boost::thread t([]{ std::cout << "Threading with Boost"; });
t.join();Certainly! Here are some additional examples of how Boost provided functionality before they were standardized in C++11 and later versions:
12- Function Objects
C++11: std::function
Boost: boost::function
- Boost offered
boost::functionto store callable objects.
Example:
#include <boost/function.hpp> boost::function<int(int, int)> f = std::plus<int>();
13- Bind
C++11: std::bind
Boost: boost::bind
- Boost allowed binding function arguments to create partial function applications.
Example:
#include <boost/bind.hpp> auto bound_func = boost::bind(std::plus<int>(), 10, _1); std::cout << bound_func(5); // Outputs 15
14- Optional
C++17: std::optional
Boost: boost::optional
- Boost provided
boost::optionalfor optional values, useful for functions that might not return a value.
Example:
#include <boost/optional.hpp>
boost::optional<int> maybe_value;
maybe_value = 10;
if (maybe_value) {
std::cout << *maybe_value;
}15- Any
C++17: std::any
Boost: boost::any
- Boost provided a type-safe container for single values of any type.
Example:
#include <boost/any.hpp>
boost::any value = 10;
try {
std::cout << boost::any_cast<int>(value);
} catch (boost::bad_any_cast &) {
std::cout << "Bad cast!";
}16- Variant
C++17: std::variant
Boost: boost::variant
- Boost provided a type-safe union that can hold one of several types.
Example:
#include <boost/variant.hpp> boost::variant<int, std::string> var; var = 10; std::cout << boost::get<int>(var);
17- Filesystem
C++17: std::filesystem
Boost: boost::filesystem
- Boost offered functionality for filesystem operations.
Example:
#include <boost/filesystem.hpp>
boost::filesystem::path p("/path/to/file");
if (boost::filesystem::exists(p)) {
std::cout << "File exists.";
}Conclusion
Boost has historically filled many gaps in the C++ standard library, providing advanced features and utilities that were later adopted by the C++ standard. These examples show how Boost helped C++ developers write more expressive and efficient code before the features were officially standardized in C++11 and later versions.
