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Better C – A subset of D Programming Language, Hacker News


It is straightforward to link C functions and libraries into D programs.     But linking D functions and libraries into C programs is not straightforward.     


D programs generally require:


  1. The D runtime library to be linked in, because many features of     the core language require runtime library support.

  3. The main () function to be written in D, to ensure that the required     runtime library support is properly initialized.


To link D functions and libraries into C programs, it’s necessary to only     require the C runtime library to be linked in. This is accomplished by defining     a subset of D that fits this requirement, called BetterC .     


Implementation Defined : BetterC is typically enabled by setting the – betterC     command line flag for the implementation.     


When BetterC is enabled, the predefined version D_BetterC     can be used for conditional compilation.     


An entire program can be written in BetterC by supplying a C main () function:

  extern  (C)  void  main ()  {       import  core.stdc.stdio: printf;      printf ( "Hello betterC  n" );  }  
> dmd -betterC hello.d && ./hello  Hello betterC  

Limiting a program to this subset of runtime features is useful     when targeting constrained environments where the use of such features     is not practical or possible.     


BetterC makes embedding D libraries in existing larger projects easier by:     

  1. Simplifying the process of integration at the build-system level
  3. Removing the need to ensure that Druntime is properly initialized on     calls to the library, for situations when an initialization step is not     performed or would be difficult to insert before the library is used.
  5. Mixing memory management strategies (GC manual memory management) can     be tricky, hence removing D's GC from the equation may be worthwhile sometimes.

Retained Features


Nearly the full language remains available. Highlights include:

  1. Unrestricted use of compile-time features
  3. Full metaprogramming facilities
  5. Nested functions, nested structs, delegates and lambdas
  7. Member functions, constructors, destructors, operating overloading, etc.
  9. The full module system
  11. Array slicing, and array bounds checking
  13. RAII (yes, it can work without exceptions)
  15. scope (exit)
  17. Memory safety protections
  19. Interfacing with C
  21. COM classes and C classes
  23. assert failures are directed to the C runtime library
  25. switch with strings
  27. final switch
  29. unittest
  31. printf format validation

Running unittests in - betterC

While, testing can be done without the - betterC flag, it is sometimes desirable to run the testsuite in - betterC too. unittest blocks can be listed with the

getUnitTests trait:
  unittest   {      assert  (0);  }     extern  (C)  void  main ()  {       static   foreach  (u;  __ traits  (getUnitTests,  __ traits  (parent, main)))          u ();  }  
> dmd -betterC -unittest -run test.d  dmd_runpezoXK: foo.d: 3: Assertion `0 'failed.  

However, in - betterC assert expressions don't use Druntime's assert and are directed to assert of the C runtime library instead.

Unavailable Features     

D features not available with BetterC :

  1. Garbage Collection
  3. TypeInfo and ModuleInfo
  5. Classes
  7. Built-in threading (eg core.thread )
  9. Dynamic arrays (though slices of static arrays work) and associative arrays
  11. Exceptions
  13. synchronized and core.sync
  15. Static module constructors or destructors

Copyright © - by the D Language Foundation Page generated by Ddoc on Mon Apr : : Brave Browser


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