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Provide a Virtual Method Anchor for Classes in Headers #6036

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iphydf opened this issue Mar 23, 2020 · 2 comments · Fixed by #6394
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Provide a Virtual Method Anchor for Classes in Headers #6036

iphydf opened this issue Mar 23, 2020 · 2 comments · Fixed by #6394
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C-bug The issue contains a bug report D-easy We estimate that the issue is easy to fix Good first issue This is a good issue to get started working on qTox M-architecture Category for internal architecture problems

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@iphydf
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iphydf commented Mar 23, 2020

If a class is defined in a header file and has a vtable (either it has virtual methods or it derives from classes with virtual methods), it must always have at least one out-of-line virtual method in the class. Without this, the compiler will copy the vtable and RTTI into every .o file that #includes the header, bloating .o file sizes and increasing link times.

Source: http://llvm.org/docs/CodingStandards.html#provide-a-virtual-method-anchor-for-classes-in-headers

In most cases, this is just a matter of adding an explicitly defined destructor and defining it in the .cpp file.
@sudden6 sudden6 added C-bug The issue contains a bug report D-easy We estimate that the issue is easy to fix Good first issue This is a good issue to get started working on qTox M-architecture Category for internal architecture problems labels Mar 26, 2020
@brandonmosher
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I'd like to take on this issue if no one else has started yet.

@anthonybilinski
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Go for it, AFAIK no one has.

@brandonmosher brandonmosher mentioned this issue Oct 15, 2021
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sphaerophoria pushed a commit to sphaerophoria/qTox that referenced this issue Nov 10, 2021
@sphaerophoria
refactor: Provide a Virtual Method Anchor for Classes in Headers
7beeadc 
Define at least one virtual method in polymorphic class cpp files to
improve link efficiency. Do so by defining a defaulted destructor or
another overridden virtual method in the class cpp file.
Also add explicitly defaulted copy/move constructors and assignment
operators to follow the rule of five and to avoid compiler suppression
of these functions due to the addition of a user-provided destructor.
Where neccessary, create new cpp files and add them to CMakeLists and
Testing.cmake. Set the -Wweak-vtables by default when compiling with
clang to issue warnings for new classes that do not comply with this
pattern.

See http://llvm.org/docs/CodingStandards.html#provide-a-virtual-method-anchor-for-classes-in-headers.

Fixes qTox#6036.
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refactor: Provide a Virtual Method Anchor for Classes in Headers
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@sudden6 @anthonybilinski @iphydf @brandonmosher