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andyarvanitis edited this page · 5 revisions

Using C++ objects/APIs directly in Eero code

By default (and like Objective-C), Eero supports direct calls to C functions, allowing full access to existing C APIs and libraries.

The latest version of Eero also supports direct C++ interoperability, enabled through a special pragma:

#pragma eero "C++"

This should appear before any code or #import/#include statements. (After comments is ok).

The intent is to provide support for existing C++ APIs/libraries, not to create a new dialect of Eero. There are no major restrictions, but a few special rules and guidelines exist to prevent language conflicts and clutter.

Declaring/defining new C++ classes within Eero source files

C++ class declarations are best kept in separate headers and pulled into Eero source files via the compatibility variants of #import/#include — see Direct #import of Eero and legacy (Objective-C and C/C++) headers. However, you can declare or define C++ classes within Eero source files, with the following restrictions:

  • C++ class member functions cannot have inline definitions; they must be defined outside of the declarations.

  • There is a keyword conflict when using class for forward declarations, but you can still forward declare C++ classes using the struct keyword, since there are no semantic differences between it and C++'s class.

C++ lambdas

C++'s lambda syntax is not supported. However, you can simply use blocks instead, since the compiler implicitly converts them to lambdas:

std::vector<int> v
...
std::for_each( v.begin(), v.end(), ^(int x | cout << x << endl) )

Exceptions

Eero recognizes try and catch as language keywords, so there is no syntactic way to distinguish between Objective-C and C++ exception handlers. However, Eero supports C++ exception handling seamlessly by allowing the mixing of Objective-C and C++ catch statements*:

try
  Log('trying...')
  // id elem = objcArray[20] // uncomment this line to see objc exception thrown
  stlString.substr(1000, 1001) // throws C++ exception

catch std::range_error& e
  Log('caught C++ range exception')

catch std::exception& e  // handle all other C++ (STL) exceptions
  Log('caught C++ exception: %s', e.what())

catch Exception e  // handle objc exceptions
  Log('Caught %@ => %@', e name, e reason)

catch ... // handle exceptions of any sort not caught previously
  Log('caught "...!"')

* Requires appropriate runtime, which includes (but is not necessarily limited to) iOS and 64-bit OS X.

C++11 range-based for loops

These are supported whenever the C++ pragma is in effect (and no C++11 compiler warning will be issued). There is one syntactic difference, however; the in keyword is used instead of the colon between the loop variable declaration and the range object expression:

std::vector<int> v
...
for int i in v
  Log( 'Vector item: %d', i ) 

The compiler knows when the in is followed by an Objective-C object, NSRange, C++ range, or C-array, and produces the appropriate results. Thus this feature is supported without introducing yet another for loop syntax.

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