Which Boost features overlap with C++11?

Question

I put my C++ skills on the shelf several years ago and it seems now, when I need them again, the landscape has changed.

We have got C++11 now, and my understanding is that it overlaps many Boost features.

Is there some summary where those overlaps lie, which Boost libraries going to become legacy, recommendation of which C++11 features to use instead of boost ones and which better not?

Answer 1

Replaceable by C++11 language features or libraries

• Foreach → range-based for
• Functional/Forward → Perfect forwarding (with rvalue references, variadic templates and std::forward)
• In Place Factory, Typed In Place Factory → Perfect forwarding (at least for the documented use cases)
• Lambda → Lambda expression (in non-polymorphic cases)
• Local function → Lambda expression
• Min-Max → std::minmax, std::minmax_element
• Ratio → std::ratio
• Static Assert → static_assert
• Thread → <thread>, etc (but check this question).
• Typeof → auto, decltype
• Value initialized → List-initialization (§8.5.4/3)
• Math/Special Functions → <cmath>, see the list below
  • gamma function (tgamma), log gamma function (lgamma)
  • error functions (erf, erfc)
  • log1p, expm1
  • cbrt, hypot
  • acosh, asinh, atanh

TR1 (they are marked in the documentation if those are TR1 libraries)

• Array → std::array
• Bind → std::bind
• Enable If → std::enable_if
• Function → std::function
• Member Function → std::mem_fn
• Random → <random>
• Ref → std::ref, std::cref
• Regex → <regex>
• Result Of → std::result_of
• Smart Ptr → std::unique_ptr, std::shared_ptr, std::weak_ptr (but boost::intrusive_ptr still cannot be replaced)
• Swap (swapping arrays) → std::swap
• Tuple → std::tuple
• Type Traits → <type_traits>
• Unordered → <unordered_set>, <unordered_map>

Features back-ported from C++11:

• Atomic ← std::atomic
• Chrono ← <chrono> (see below)
• Move ← Rvalue references

Replaceable by C++17 language features:

• String_ref → std::string_view
• Filesystem → <filesystem> (Filesystem TS)
• Optional → std::optional (Library Fundamentals TS v1)
• Any → std::any (Library Fundamentals TS v1)
• Math/Special Functions → <cmath> (Special Math IS), see the list below
  • beta function
  • (normal / associated / spherical) Legendre polynomials
  • (normal / associated) Legendre polynomials
  • Hermite polynomials
  • Bessel (J / Y / I / K) functions (Y is called Neumann function in C++)
  • spherical Bessel (j / y) functions
  • (incomplete / complete) elliptic integrals of (first / second / third kind)
  • Riemann zeta function
  • exponential integral Ei
• Variant → std::variant (P0088R2)

The standard team is still working on it:

• Math Common Factor → std::experimetal::gcd, lcm (Library Fundamentals TS v2)
• Concept check → Concepts TS
• Range → Range TS
• Asio → Networking TS (sockets and timers only)
• Multiprecision → Numerics TS
• Coroutine/Coroutine2 → Coroutines TS

A large part of MPL can be trimmed down or removed using variadic templates. Some common use cases of Lexical cast can be replaced by std::to_string and std::stoX.

Some Boost libraries are related to C++11 but also have some more extensions, e.g. Boost.Functional/Hash contains hash_combine and related functions not found in C++11, Boost.Chrono has I/O and rounding and many other clocks, etc. so you may still want to take a look at the boost ones before really dismissing them.

Answer 2

Actually, I don't think the boost libraries are going to become legacy.

Yes, you should be able to use std::type_traits, regex, shared_ptr, unique_ptr, tuple<>, std::tie, std::begin instead of Boost Typetraits/Utility, Boost Smartpointer, Boost Tuple, Boost Range libraries, but there should in practice be no real need to 'switch' unless you are moving more of your code to c++11.

Also, in my experience, the std versions of most of these are somewhat less featureful. E.g. AFAICT the standard does not have

• Perl5 regular expressions
• call_traits
• Certain regex interface members (such as bool boost::basic_regex<>::empty()) and othe interface differences
  • this bites more since the Boost interface is exactly matched with Boost Xpressive
  • and it plays much more nicely with Boost String Algorithms Obviously, the latter don't have standard counterparts (yet?)
• Many things relating to TMP (Boost Fusion)

• Lazy, expression template-based lambdas; they have inevitable benefits in that they can be polymorphic today, as opposed to C++11. Therefore they can often be more succinct:

   std::vector<int> v = {1,2,-9,3};
  
   for (auto i : v | filtered(_arg1 >=0))
       std::cout << i << "\n";
  
   // or:
   boost::for_each(v, std::cout << _arg1);
  

  Most definitely, this still has some appeal over C++11 lambdas (with trailing return types, explicit capturing and declared parameters).

Also, there is a BIG role for Boost, precisely in facilitating path-wise migration from C++03 to C++11 and integrating C++11 and C++03 codebases. I'm particularly thinking of

• Boost Auto (BOOST_AUTO)
• Boost Utility (boost::result_of<> and related)
• Boost Foreach (BOOST_FOREACH)
• Don't forget: Boost Move - which makes it possible to write classes with move semantics with a syntax that will compile equally well on C++03 compilers with Boost 1_48+ and C++11 compilers.

Just my $0.02