[libcamera-devel] [PATCH 1/2] meson.build: Switch to C++14

[Kieran Bingham]

Hi Laurent,

On 14/01/2020 00:15, Laurent Pinchart wrote:
> C++14 is a minor release that doesn't introduce major new concepts or
> paradigms compared to C++11, but brings two useful changes for us:
> 
> - std::make_unique allows dropping our custom implementation in utils.
> - Functions returning constexpr are not assumed to be const anymore,
>   which is needed to create a standard-conformant span implementation.
> 
> All the g++ and clang++ versions we support and test (g++-5 onwards and
> clang++6 onwards) support C++14. However, due to a defect in the
> original C++14 specification, solved in N4387 ([1]), compilation would
> fail on g++-5 due to the use of std::map::emplace() with a non-copyable
> value type. It turns out we can easily fix it by switching to the
> explicit piecewise emplace() overload.

Eeep. That's a bit of a pain, but a short fix is helpful.

And we get to progress the defined standard.

> There is thus really nothing holding back the switch. Let's do it, and
> update the coding style accordingly.
> 

\o/

> [1] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4387
> 

All LGTM.

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>


> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  Documentation/coding-style.rst | 23 +++++++++--------------
>  meson.build                    |  2 +-
>  src/ipa/rkisp1/rkisp1.cpp      |  4 +++-
>  3 files changed, 13 insertions(+), 16 deletions(-)
> 
> diff --git a/Documentation/coding-style.rst b/Documentation/coding-style.rst
> index 9939c7b1e86d..bbc1f2fb18c6 100644
> --- a/Documentation/coding-style.rst
> +++ b/Documentation/coding-style.rst
> @@ -86,22 +86,17 @@ headers, and with double quotes for other libcamera headers.
>  C++ Specific Rules
>  ------------------
>  
> -The code shall be implemented in C++03, extended with the following
> -C++-11-specific features:
> -
> -* Initializer lists
> -* Type inference (auto and decltype)
> -  Type inference shall be used with caution, to avoid drifting towards an
> -  untyped language.
> -* Range-based for loop
> -* Lambda functions
> -* Explicit overrides and final
> -* Null pointer constant
> -* General-purpose smart pointers (std::unique_ptr), deprecating std::auto_ptr.
> +The code shall be implemented in C++14, with the following caveats:
> +
> +* Type inference (auto and decltype) shall be used with caution, to avoid
> +  drifting towards an untyped language.
> +* The explicit, override and final specifiers are to be used where applicable.
> +* General-purpose smart pointers (std::unique_ptr) deprecate std::auto_ptr.
>    Smart pointers, as well as shared pointers and weak pointers, shall not be
>    overused.
> -* Variadic class and function templates
> -* rvalue references, move constructor and move assignment
> +* Classes are encouraged to define move constructors and assignment operators
> +  where applicable, and generally make use of the features offered by rvalue
> +  references.
>  
>  Object Ownership
>  ~~~~~~~~~~~~~~~~
> diff --git a/meson.build b/meson.build
> index 634488589a46..37cf4d665f7b 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -4,7 +4,7 @@ project('libcamera', 'c', 'cpp',
>      default_options : [
>          'werror=true',
>          'warning_level=2',
> -        'cpp_std=c++11',
> +        'cpp_std=c++14',
>      ],
>      license : 'LGPL 2.1+')
>  
> diff --git a/src/ipa/rkisp1/rkisp1.cpp b/src/ipa/rkisp1/rkisp1.cpp
> index 74b2922004be..a8dd1645d3e8 100644
> --- a/src/ipa/rkisp1/rkisp1.cpp
> +++ b/src/ipa/rkisp1/rkisp1.cpp
> @@ -104,7 +104,9 @@ void IPARkISP1::configure(const std::map<unsigned int, IPAStream> &streamConfig,
>  void IPARkISP1::mapBuffers(const std::vector<IPABuffer> &buffers)
>  {
>  	for (const IPABuffer &buffer : buffers) {
> -		auto elem = buffers_.emplace(buffer.id, buffer.planes);
> +		auto elem = buffers_.emplace(std::piecewise_construct,
> +					     std::forward_as_tuple(buffer.id),
> +					     std::forward_as_tuple(buffer.planes));
>  		const FrameBuffer &fb = elem.first->second;
>  
>  		/*
> 

-- 
Regards
--
Kieran