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refactor: remove dependency on boost.tti using detector idiom#531

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Becheler merged 1 commit into
boostorg:developfrom
Becheler:refactor/drop-tti-dependency
Jul 20, 2026
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refactor: remove dependency on boost.tti using detector idiom#531
Becheler merged 1 commit into
boostorg:developfrom
Becheler:refactor/drop-tti-dependency

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@Becheler

@Becheler Becheler commented Jul 17, 2026

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Remove dependency to Boost.TTI. Use void_t detector idiom instead.

Before submitting

  • This PR targets the develop branch.
  • I searched for an existing PR or issue covering the same change.
  • My contribution is licensed under the Boost Software License 1.0.

Type of change

  • Bug fix
  • New feature or API addition
  • Refactor (no behavior change)
  • Documentation
  • Build, CI, or tooling
  • Other (specify below)

Does this PR introduce a breaking change?

  • Yes (describe migration impact below)
  • No

What this PR does

Removes Boost.Graph's dependency on Boost.TTI (and the last MPL use in DFS).

  • depth_first_search.hpp: replaced the BOOST_TTI_HAS_MEMBER_FUNCTION(finish_edge) detector and its __GNUC__/clang/intel #if fork with a void_t expression-SFINAE detector, has_finish_edge<Vis, E, G>, that checks whether vis.finish_edge(e, g) is a valid call. D
  • dropped #include <boost/tti/has_member_function.hpp>
  • added <boost/type_traits/make_void.hpp> and <type_traits>.
  • This also removes the mpl::vector<E, const G&> that only existed to feed TTI's signature, so the file is now MPL-free as well.
  • build.jam: dropped /boost/tti//boost_tti.
  • CMakeLists.txt: dropped Boost::tti.

All changes in boost::detail, detection is identical for void finish_edge(Edge, const Graph&) visitors, and the check now works uniformly on C++14 compilers.

Motivation

It's not worth pulling a Boost dependency anymore now that the sfinae + detector idiom are available in C++14.

Testing

Checklist

  • Existing tests pass (b2 in the test/ directory).
  • New behavior is covered by a test, or this is a docs / build / refactor change.
  • Documentation was updated if user-facing behavior changed.
  • No new compiler warnings on the platforms I built against.

@Becheler Becheler self-assigned this Jul 17, 2026
@Becheler Becheler added the technical debt Code that works but needs refactoring, cleanup, or modernization. Not user-facing. label Jul 17, 2026
@github-actions

github-actions Bot commented Jul 17, 2026

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Compiler-warning counts vs develop (auto-generated).
PR run 29568558245 vs develop run 29503421610 (b3cb64738b).

Job Baseline After Delta
macos (clang, 14) 4 4 0
macos (clang, 17) 4 4 0
macos (clang, 20) 4 4 0
ubuntu (clang-19, 14) 4 4 0
ubuntu (clang-19, 17) 4 4 0
ubuntu (clang-19, 20) 4 4 0
ubuntu (clang-19, 23) 4 4 0
ubuntu (gcc-14, 14) 10 10 0
ubuntu (gcc-14, 17) 10 10 0
ubuntu (gcc-14, 20) 10 10 0
ubuntu (gcc-14, 23) 10 10 0
windows_msvc_14_3 (msvc-14.3) 971 971 0

@github-actions

github-actions Bot commented Jul 17, 2026

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Boost dependency footprint vs develop (auto-generated).
PR run 29568558172 vs develop run 29503421582 (b3cb64738b).

Header-inclusion weights (graph files pulling each direct dependency in):

Dependency develop PR Δ
tti 1 0 -1
type_traits 40 41 +1

Transitive Boost modules: 69 → 68 (-1)

  • removed: tti

@Becheler
Becheler marked this pull request as ready for review July 17, 2026 11:05
@Becheler
Becheler requested a review from jeremy-murphy as a code owner July 17, 2026 11:05
@jeremy-murphy

jeremy-murphy commented Jul 20, 2026

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Did you mean to add the Boost type_traits dependency?

@Becheler

Becheler commented Jul 20, 2026 •
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Yes:

  • the #include <boost/type_traits/make_void.hpp>is for boost::void_t (there are special portability cases the boost implem handles)
  • the #include <type_traits> is for std::false_type

The simplest implementation of the detector idiom has some edge cases ( http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4502.pdf )

This definition relies on the resolution of CWG issue 1558 (“The treatment of unused arguments in an alias template specialization is not specified by the current wording of 14.5.7 [temp.alias]”) adopted at the Urbana meeting.

Boost implementation goes through an auxiliary boost::make_void class in order to solve this issue
https://www.boost.org/doc/libs/latest/libs/type_traits/doc/html/boost_typetraits/reference/make_void.html

@Becheler
Becheler merged commit dbca3f1 into boostorg:develop Jul 20, 2026
27 of 28 checks passed
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