Comments (5)
@tomjwaldron: Agreed, and expected. Here's your example reduced even further: https://godbolt.org/z/6Wac8s938
stdext::inplace_function<void()> f;
stdext::inplace_function<void()> g = f; // OK
stdext::inplace_function<void()> h = [f]() { f(); }; // error
Since inplace_function
doesn't heap-allocate, it needs to have enough room inside its own memory footprint to store whatever callable you're putting into it. If you put in something bigger than the inplace_function
itself (such as a lambda capturing an inplace_function
by value), then of course that won't work — and inplace_function
specifically refuses to heap-allocate any more space to hold that big callable. (Its stubborn compile-time refusal to heap-allocate is "a feature, not a bug.")
One way to (work around, fix) your original code would be to make two sizes of type-erased functions: one to hold callbacks, and one to hold lambdas-that-capture-the-first-kind. https://godbolt.org/z/9xEYPM75W
using SmallerEventFunction = stdext::inplace_function<void()>;
using EventFunction = stdext::inplace_function<void(), sizeof(SmallerEventFunction)>;
This guarantees that std::is_constructible_v<EventFunction, SmallerEventFunction>
.
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I can generate some example cases if you guys are unaware of this circumstance
Yes please. http://sscce.org
inplace_function
should only ever need ~16 bytes more Capacity
than the sizeof
the object you're trying to store in it. So it should never require Capacity=10000
unless you're trying to store something big — like, say, [r = std::mt19337()]() { return r(); }
.
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@victorstewart, were you able to reproduce the issue?
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sorry! been so busy with my beta :). i’ll get you those test cases this weekend
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I ran into this issue. Might be a little contrived, I'm not sure, but here's an example where std::function works fine but stdext::inplace_function doesn't: https://godbolt.org/z/KcfYsvd15
error: static_assert failed due to requirement 'sizeof((lambda at <source>:26:21)) <= 32UL' "inplace_function cannot be constructed from object with this (large) size"
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Related Issues (20)
- [slot_map] constructors HOT 1
- [inplace_function] benchmark HOT 4
- [slot_map] Can you get a key using an iterator? HOT 5
- [slot_map] R1/R2 criticisms HOT 12
- [inplace_function] Ambiguous overloads. HOT 5
- [inplace_function] Should [](){return 42;} be convertible to inplace_function<void()>? HOT 1
- [inplace_function] make it usable without exceptions HOT 2
- inplace_function doesn't handle arguments with rvalue references well HOT 1
- [inplace function] Problems assigning if my starting point is empty/nullptr HOT 4
- [inplace_function] Const-callability means thread-safety HOT 4
- volatile inplace_function fails to compile HOT 6
- License is missing on some includes HOT 1
- `sg14::ring_span`: clear () member function gone awol HOT 2
- [inplace_function] Opt-in "safe" default constructed inplace_function HOT 7
- Provide CMake & Conan installation support
- slot_map: custom key causing clang to seg fault. HOT 1
- [inplace_function] usage at shared library boundaries HOT 5
- sg14::span_ring: class template argument deduction
- [inplace_function.h] Copyright holder HOT 3
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