digitalmars.D - Another use for static ifs
- Unknown W. Brackets (65/65) Jun 19 2005 We currently have:
- Walter (6/11) Jun 19 2005 You can already do it:
- Unknown W. Brackets (25/44) Jun 20 2005 Typeof, eh? I noticed you could do &foo, but that of course fails if
- Walter (6/29) Jun 25 2005 Good catch, I'll fix it.
We currently have:
static if (some_const == 5)
static if (is(bar T))
As I mentioned before (before static if), I think it would be very
useful to be able to check, with static if or similar, for the existence
of functions.
I don't mean linking. I just mean checking if a function was defined
yet. In its basic form, this doesn't seem that great:
version (Windows)
import std.c.windows.windows;
else version (linux)
import std.c.linux.linux;
...
static if (GetCurrentThreadId) // or defined(GetCurrentThreadId), etc.
id = GetCurrentThreadId(...);
else
id = pthread_self();
However, it becomes more apparent with a longer example:
version (Windows)
import std.c.windows.windows;
else version (linux)
import std.c.linux.linux;
else version (macosx)
import std.c.macosx.macosx;
else version (beos)
import std.c.beos.beos;
...
static if (GetCurrentThreadId)
id = GetCurrentThreadId(...);
else
id = pthread_self();
Of course, this can be handled by an alias. But, watch this:
...
static if (!stricmp)
{
int stricmp(char[] s1, char[] s2)
{
...
}
}
That comes right from gnuc.c in D's source. Obviously, D wants to avoid
problems where one operating system or vendor defines a function, and
another doesn't... but I think it will prove inevitable.
At least with a way to know if things are defined *which doesn't depend
on an import always having the same functions forever and everywhere*
it's much more possible to handle both versioning, OS, and vendor
problems. This will of course depend on the .lib or .a file containing
the functions listed in the import, but for my purposes I'm assuming
*that* will always be true.
And, the last use is as I mentioned in the above paragraph: handling
different versions of D. For example, let's say someone ported the DMD
compiler (or GDC, whatever) to another system... let's say to a gaming
console, like Sony's. If I wanted my program to compile on their
(probably old) version of D, with their probably old phobos, I would be
able to use the above for things added to phobos I want to use.
Without this, the above situation would be sticky indeed. There's no
way to know the current D version in the code, afaik, currently... so I
would just have to tell the person that they're going to have to wait
for the person who ported it to update it (or tell them to *try*
compiling the new phobos with their old version.)
That said, maybe it seems like that situation is a bit far fetched...
and this doesn't handle !is or anything. Still, I think it would be
helpful - even if D somehow convinces everyone who's made autoconf
necessary to make amends.
-[Unknown]
Jun 19 2005
"Unknown W. Brackets" <unknown simplemachines.org> wrote in message news:d93ka0$241e$3 digitaldaemon.com...As I mentioned before (before static if), I think it would be very useful to be able to check, with static if or similar, for the existence of functions. I don't mean linking. I just mean checking if a function was defined yet. In its basic form, this doesn't seem that great:You can already do it: static if (typeof(foo)) ... will be false if foo is not defined, and true if it is.
Jun 19 2005
Typeof, eh? I noticed you could do &foo, but that of course fails if it's not defined with a compiler error. Is this documented? As I said, it seems like a very useful thing to use in many cases. By the way: (found while checking again...) http://www.digitalmars.com/d/declaration.html#typeof printf("%d\n", typeof('c').size); // prints 1 Should be: printf("%d\n", typeof('c').sizeof); // prints 1 And: int[typeof[p]] a; // a is of type int[int*] Should be (?): int[typeof(p)] a; // a is of type int[int*] Anyway, I can't get it to work. I just get errors.... static if (typeof(foo)) found ')' when expecting '.' following 'typeof(foo)' static if (typeid(typeof(foo))) undefined identifier foo static if (typeof(foo).sizeof != 0) undefined identifier foo But, I like the syntax. I thought adding "defined" or something was bad, and I thought leaving it bare was ugly... typeof really makes it work. If only it'd compile for me :). May I suppose this is something changed for 0.128, then? -[Unknown]"Unknown W. Brackets" <unknown simplemachines.org> wrote in message news:d93ka0$241e$3 digitaldaemon.com...As I mentioned before (before static if), I think it would be very useful to be able to check, with static if or similar, for the existence of functions. I don't mean linking. I just mean checking if a function was defined yet. In its basic form, this doesn't seem that great:You can already do it: static if (typeof(foo)) ... will be false if foo is not defined, and true if it is.
Jun 20 2005
"Walter" <newshound digitalmars.com> "Unknown W. Brackets" <unknown simplemachines.org> wrote in message news:d9654v$l5k$1 digitaldaemon.com...Typeof, eh? I noticed you could do &foo, but that of course fails if it's not defined with a compiler error. Is this documented? As I said, it seems like a very useful thing to use in many cases. By the way: (found while checking again...) http://www.digitalmars.com/d/declaration.html#typeof printf("%d\n", typeof('c').size); // prints 1 Should be: printf("%d\n", typeof('c').sizeof); // prints 1 And: int[typeof[p]] a; // a is of type int[int*] Should be (?): int[typeof(p)] a; // a is of type int[int*]Good catch, I'll fix it.Anyway, I can't get it to work. I just get errors.... static if (typeof(foo)) found ')' when expecting '.' following 'typeof(foo)' static if (typeid(typeof(foo))) undefined identifier foo static if (typeof(foo).sizeof != 0) undefined identifier foo But, I like the syntax. I thought adding "defined" or something was bad, and I thought leaving it bare was ugly... typeof really makes it work. If only it'd compile for me :).Arggh, I goofed. It should be: static if ( is(typeof(foo)) ) ...
Jun 25 2005