Re: Question about version ( ) keyword

[Daniel Kozak via Digitalmars-d]

Dne 21.3.2016 v 15:51 Vincent R via Digitalmars-d napsal(a):
Hi,

When looking at core definitions like core.sys.posix.pthread I can see 
some "duplicated" code because it seems version doesn't support Or as 
we would do in C/C++ with #ifdefined.
For instance if can read this:

version( CRuntime_Glibc )
{
    enum PTHREAD_BARRIER_SERIAL_THREAD = -1;

    int pthread_barrier_destroy(pthread_barrier_t*);
    int pthread_barrier_init(pthread_barrier_t*, in 
pthread_barrierattr_t*, uint);
    int pthread_barrier_wait(pthread_barrier_t*);
    int pthread_barrierattr_destroy(pthread_barrierattr_t*);
    int pthread_barrierattr_getpshared(in pthread_barrierattr_t*, int*);
    int pthread_barrierattr_init(pthread_barrierattr_t*);
    int pthread_barrierattr_setpshared(pthread_barrierattr_t*, int);
}
else version( FreeBSD )
{
    enum PTHREAD_BARRIER_SERIAL_THREAD = -1;

    int pthread_barrier_destroy(pthread_barrier_t*);
    int pthread_barrier_init(pthread_barrier_t*, in 
pthread_barrierattr_t*, uint);
    int pthread_barrier_wait(pthread_barrier_t*);
    int pthread_barrierattr_destroy(pthread_barrierattr_t*);
    int pthread_barrierattr_getpshared(in pthread_barrierattr_t*, int*);
    int pthread_barrierattr_init(pthread_barrierattr_t*);
    int pthread_barrierattr_setpshared(pthread_barrierattr_t*, int);
}
else version (OSX)
{
}
else version (Solaris)
{
    enum PTHREAD_BARRIER_SERIAL_THREAD = -2;

    int pthread_barrier_destroy(pthread_barrier_t*);
    int pthread_barrier_init(pthread_barrier_t*, in 
pthread_barrierattr_t*, uint);
    int pthread_barrier_wait(pthread_barrier_t*);
    int pthread_barrierattr_destroy(pthread_barrierattr_t*);
    int pthread_barrierattr_getpshared(in pthread_barrierattr_t*, int*);
    int pthread_barrierattr_init(pthread_barrierattr_t*);
    int pthread_barrierattr_setpshared(pthread_barrierattr_t*, int);
}
else version (CRuntime_Bionic)
{
}
else
{
    static assert(false, "Unsupported platform");
}

When I see this code I cannot help thinking of something like:

version( CRuntime_Glibc ) || version( FreeBSD ) || version (Solaris)
{
    if(version(Solaris))
       enum PTHREAD_BARRIER_SERIAL_THREAD = -2;
    else
       enum PTHREAD_BARRIER_SERIAL_THREAD = -1;

    int pthread_barrier_destroy(pthread_barrier_t*);
    int pthread_barrier_init(pthread_barrier_t*, in 
pthread_barrierattr_t*, uint);
    int pthread_barrier_wait(pthread_barrier_t*);
    int pthread_barrierattr_destroy(pthread_barrierattr_t*);
    int pthread_barrierattr_getpshared(in pthread_barrierattr_t*, int*);
    int pthread_barrierattr_init(pthread_barrierattr_t*);
    int pthread_barrierattr_setpshared(pthread_barrierattr_t*, int);
}
else version (OSX) ||version (CRuntime_Bionic)
{
}
else
{
    static assert(false, "Unsupported platform");
}

I suppose language creators had good reasons to not allow it but I am 
a bit disapointed by the aspect of this language because some files 
are really verbose.
However I understand that this limitation allow a clear separation 
between different platforms...
It is already has been sad why this does not work. But you can still do 
something like this (or maybe even something better(shorter)):

version(CRuntime_Glibc)
{
    enum PTHREAD_BARRIER_SERIAL_THREAD = -1;
    version = WhatEver1;
}
else version(FreeBSD)
{
    enum PTHREAD_BARRIER_SERIAL_THREAD = -1;
    version = WhatEver1;
}
else version (OSX)
{
    version = WhatEver2;
}
else version (Solaris)
{
    enum PTHREAD_BARRIER_SERIAL_THREAD = -2;
    version = WhatEver1;
}
else version (CRuntime_Bionic)
{
    version = WhatEver2;
}
version (WhatEver1)
{
    int pthread_barrier_destroy(pthread_barrier_t*);
    int pthread_barrier_init(pthread_barrier_t*, in 
pthread_barrierattr_t*, uint);
    int pthread_barrier_wait(pthread_barrier_t*);
    int pthread_barrierattr_destroy(pthread_barrierattr_t*);
    int pthread_barrierattr_getpshared(in pthread_barrierattr_t*, int*);
    int pthread_barrierattr_init(pthread_barrierattr_t*);
    int pthread_barrierattr_setpshared(pthread_barrierattr_t*, int);
}
else version (WhatEver2)
else
{
    static assert(false, "Unsupported platform");
}


But to be fair I still prefer original code because it is obvious, which 
platform support what :)