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author | Thiago Marcos P. Santos <tmpsantos@gmail.com> | 2020-02-07 18:57:44 +0200 |
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committer | Thiago Marcos P. Santos <tmpsantos@gmail.com> | 2020-02-07 20:12:44 +0200 |
commit | 97cab6365bd083d162544eb4bcae4ebd47a7ecae (patch) | |
tree | dd64791f07e0a111356c546069a500f930a1e896 /DEVELOPING.md | |
parent | 021e48f35e4812803ecaadb1ed262c83354b767e (diff) | |
download | qtlocation-mapboxgl-97cab6365bd083d162544eb4bcae4ebd47a7ecae.tar.gz |
[documentation] Updated README and DEVELOPING
To reflect changes in the buildsystem.
Diffstat (limited to 'DEVELOPING.md')
-rw-r--r-- | DEVELOPING.md | 175 |
1 files changed, 9 insertions, 166 deletions
diff --git a/DEVELOPING.md b/DEVELOPING.md index d865a35d2d..3dea887120 100644 --- a/DEVELOPING.md +++ b/DEVELOPING.md @@ -1,168 +1,11 @@ -# Modern C++ support +# Developing -Mapbox GL Native supports the C++14 standard, and encourages contributions to -the source code using modern C++ idioms like return type deductions, generic -lambdas, `std::optional` and alike. However, we do not support all the features -from the final draft of the C++14 standard - we had to sacrifice support for -these features in order to support GCC from version 4.9 onwards. +This is been rewritten to include: -The following C++14 features are **not supported** in Mapbox GL Native: - -## [C++14 variable templates](https://isocpp.org/wiki/faq/cpp14-language#variable-templates) - -Constructs like the example below are not supported: - -```C++ -template<typename T> constexpr T pi = T(3.14); -``` - -### Workarounds: - -- If the variable is an alias, use the call the alias points to: [example](https://github.com/mapbox/mapbox-gl-native/commit/f1ac757bd28351fd57113a1e16f6c2e00ab193c1#diff-711ce10b54a522c948efc9030ffab4fcL269) -```C++ -// auto foo = pi<double>; -auto foo = double(3.14); -``` - -- Replace variable templates with either functions or structs: [example 1](https://github.com/mapbox/mapbox-gl-native/commit/f1ac757bd28351fd57113a1e16f6c2e00ab193c1#diff-ffbe6cdfd30513aaa4749b4d959a5da6L58), [example 2](https://github.com/mapbox/mapbox-gl-native/commit/f1ac757bd28351fd57113a1e16f6c2e00ab193c1#diff-04af54dc8685cdc382ebe24466dc1d00L98) - -## [C++14 aggregates with non-static data member initializers](http://en.cppreference.com/w/cpp/language/aggregate_initialization) - -Constructs like the example below are not supported: - -```C++ -struct Foo { - int x = { 0 }; -}; - -// error: no matching function for call to 'Foo::Foo(<brace-enclosed initializer list>)' -int main() { - Foo foo { 0 }; - return 0; -} -``` - -### Workarounds -- Replace data member initializers with default parameter values in default constructors: - -```C++ -struct Foo { - Foo(int x_ = 0) : x(x_) {} - int x; -}; - -int main() { - Foo foo { 0 }; // works with default constructor - return 0; -} -``` - -- Replace bracket initialization with regular round brackets or none: - -```C++ -struct Foo { - Foo(int x_ = 0) : x(x_) {} - int x; -}; - -int main() { - Foo foo(); // works - Foo bar; // also works - return 0; -} -``` - -## [Extended `constexpr` support](https://isocpp.org/wiki/faq/cpp14-language#extended-constexpr) - -GCC 4.9 strictly forbids `constexpr` usage in the following scenarios: -- No local variable declarations (not `static` or `thread_local`, and no uninitialized variables) -- Cannot mutate objects whose lifetime began with the constant expression evaluation -- Disable usage of if, switch, for, while, do-while (not goto) inside constexpr expressions -- Enforces that constexpr member functions are implicitly const - -```C++ -// sorry, unimplemented: use of the value of the object being constructed -// in a constant expression -struct Foo { - int x, y; - constexpr Foo(int i) : x(i), y(x) {} -}; - -// error: body of constexpr function 'constexpr int test1(int)' not a -// return-statement -constexpr int test1(int i) { - int j = i; - return j; -} - -// error: body of constexpr function 'constexpr bool test2(int)' not a -// return-statement -constexpr bool test2(int i) { - if (i > 0) { - return true; - } else { - return false; - } -} -``` - -### Workarounds - -- Either remove `constexpr` specifier or replace it with `inline` in case of - functions - - -## [Polymorphic lambdas](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68278) - -GCC 5.2.0 crashes with polymorphic lambdas and this version of the compiler -is currently used in Qt Automotive. Luckily polymorphic lambdas are rarely -used/needed but we had one incident fixed by #9665. - -### Workarounds - -- Copy & Paste™ the code. - - -## [Inheriting Constructors](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2540.htm) - -Compilers with only partial C++11 support causes compilation errors when using-declaration is used in derived class to inherit its base class's constructors `(e.g. using Base::Base;)`. - -```C++ -#include <vector> - -template <typename T> -struct Varargs : std::vector<T> -{ - using std::vector<T>::vector; -}; - -// error: conflicts with version inherited from 'std::__1::vector<int, std::__1::allocator<int> >' -int main() -{ - Varargs<int> v; - return 0; -} -``` - -### Workarounds - -- Replace using-declaration (e.g. using Base::Base;) in derived class with `universal forwarding constructor`. - -```C++ -#include <vector> - -template <typename T> -struct Varargs : std::vector<T> -{ - template <class... Args> - Varargs(Args&&... args) : std::vector<T>(std::forward<Args>(args)...) {} -}; - -int main() -{ - Varargs<int> v; - return 0; -} -``` - -Note: Using `universal forwarding constructor` may not be appropriate when derived class has additional members that are not in base class. Write constructors for the derived class explicitly instead of using `universal forwarding constructor` when the derived class has additional members. +- How to build for the platforms we support. +- Acceptance criteria for code contributions (style, static asserts) +- How to run the unit tests. +- How to run the benchmarks. +- How to run the render tests. +- How to rebaseline baselines metrics. +- How to use GL Native as a 3rd party library in your project. |