fix dangling reference in pool_type_impl<T&> init constructor (#504)#674
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kris-jusiak merged 1 commit intoMay 23, 2026
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LGTM, thanks, there is merge conflict though, coule you rebase |
…oost-ext#504) The pool_type_impl<T&> specialisation (active under BOOST_SML_CREATE_DEFAULT_CONSTRUCTIBLE_DEPS) had a copy-paste bug in the constructor that accepts an (init, object) pair: constexpr pool_type_impl(const init &i, const TObject &object) : value(i, object) {} 'value' is a T& reference member. In a member-initialiser list the expression 'value(i, object)' for a reference type does NOT call a two-argument constructor; it applies the C++ comma operator — evaluates i (discarding the result), evaluates object, and binds 'value' to the result. 'object' is a function parameter (const TObject&) which goes out of scope once the constructor returns, leaving 'value' as a dangling reference. Fix: initialise the backing-store member value_ by extracting the T from the source pool via try_get, then bind the reference member value to value_: constexpr pool_type_impl(const init &, const TObject &object) : value_{try_get<T>(&object)}, value{value_} {} This stores a local copy in value_ and keeps the reference valid for the lifetime of the pool_type_impl object. Regression test added in test/ft/dependencies.cpp: ref_dep_copy_from_pool_not_dangling — SM with reference dep + sub-SM exercises the pool(const pool<TArgs...>&) path that instantiates the fixed constructor. Fixes boost-ext#504.
PavelGuzenfeld
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On it. |
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I'm also making sure the CI runs green. If its possible please wait till all is GO next time. |
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Problem
The
pool_type_impl<T&>specialisation (active underBOOST_SML_CREATE_DEFAULT_CONSTRUCTIBLE_DEPS) contains a copy-paste bug in its(init, object)constructor:valueis aT&(reference) member. In a member-initialiser list,value(i, object)for a reference type does not call a two-argument constructor — it applies the C++ comma operator: evaluatesi(discards result), then evaluatesobject, and bindsvalueto the result.objectis a function parameter (const TObject&) that goes out of scope once the constructor returns, leavingvalueas a dangling reference. Any subsequent access throughvalueis undefined behaviour.Fix
Initialise the backing-store member
value_by extractingTfrom the source pool viatry_get, then bind the reference membervaluetovalue_:This stores a local copy in
value_and keeps the reference valid for the lifetime of thepool_type_implobject — matching the pattern already used in the other constructors of this specialisation.Test
Regression test
ref_dep_copy_from_pool_not_danglingadded intest/ft/dependencies.cpp: an SM with a reference dep (dep504&) and a sub-state machine exercises thepool(const pool<TArgs...>&)constructor path that instantiates the fixed constructor.Fixes #504.