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digitalmars.D.announce - Static Parameter Function Specialization in D

reply =?UTF-8?B?Ik5vcmRsw7Z3Ig==?= <per.nordlow gmail.com> writes:
I've read somewhere that D supports specialization of functions 
to calls where arguments are compile-time constants. Typical use 
of this is in matrix power functions (if exponent is 2 `x*x` is 
often faster than the general case).

I want this in my member function

        bool opIndexAssign(bool b, size_t i)  trusted pure nothrow 
in {
             assert(i < len);        // TODO: Add static assert(i 
< len) when i is constant
         } body {
             b ? bts(ptr, i) : btr(ptr, i);
             return b;
         }

of a statically sized `BitSet` struct I'm writing. This in order 
to, when possible, get compile-time bounds checking on the index 
variable `i`. I thought

     bool opIndexAssign(bool b, const size_t i)  trusted pure 
nothrow in {
         static assert(i < len);
     } body {
         b ? bts(ptr, i) : btr(ptr, i);
         return b;
     }

would suffice but then DMD complains as follows

     dmd -debug -gc -gs -unittest -D 
-Dd/home/per/.emacs.d/auto-builds/dmd/Debug-Boundscheck-Unittest/
ome/per/Work/justd/ 
-w -main  ~/Work/justd/bitset.d /home/per/Work/justd/assert_ex.d 
-of/home/per/.emacs.d/auto-builds/dmd/Debug-Boundscheck-Unittest/home/per/Work/justd/bitset
     /home/per/Work/justd/bitset.d(58): Error: 
bitset.BitSet!2.BitSet.opIndexAssign called with argument types 
(bool, int) matches both:
     	/home/per/Work/justd/bitset.d(49): opIndexAssign(bool b, 
ulong i)
     and:
     	/home/per/Work/justd/bitset.d(65): opIndexAssign(bool b, 
const(ulong) i)
     /home/per/Work/justd/bitset.d(66): Error: variable i cannot 
be read at compile time
     /home/per/Work/justd/bitset.d(66):        while evaluating: 
static assert(i < 2LU)
     /home/per/Work/justd/bitset.d(58): Error: 
bitset.BitSet!2.BitSet.opIndexAssign called with argument types 
(bool, int) matches both:
     	/home/per/Work/justd/bitset.d(49): opIndexAssign(bool b, 
ulong i)

Do I have to make parameter `i` a template parameter, say using 
type `U`, and then use static if `someTypeTrait!U`. I tried this 
but isMutable!Index always evaluates to true.

     import std.traits: isIntegral;
     bool opIndexAssign(Index)(bool b, Index i)  trusted pure 
nothrow if (isIntegral!Index) in {
         import std.traits: isMutable;
         // See also: 
http://stackoverflow.com/questions/19906516/static-parameter-function-specialization-in-d
         static if (isMutable!Index) {
             assert(i < len);
         } else {
             import std.conv: to;
             static assert(i < len,
                           "Index " ~ to!string(i) ~ " must be 
smaller than BitSet length " ~  to!string(len));
         }
     } body {
         b ? bts(ptr, i) : btr(ptr, i);
         return b;
     }
Nov 11 2013
next sibling parent "Xinok" <xinok live.com> writes:
On Monday, 11 November 2013 at 13:41:04 UTC, Nordlöw wrote:

 I've read somewhere that D supports specialization of functions 
 to calls where arguments are compile-time constants. Typical 
 use of this is in matrix power functions (if exponent is 2 
 `x*x` is often faster than the general case).

 I want this in my member function

        bool opIndexAssign(bool b, size_t i)  trusted pure 
 nothrow in {
             assert(i < len);        // TODO: Add static 
 assert(i < len) when i is constant
         } body {
             b ? bts(ptr, i) : btr(ptr, i);
             return b;
         }

 of a statically sized `BitSet` struct I'm writing. This in 
 order to, when possible, get compile-time bounds checking on 
 the index variable `i`. I thought

     bool opIndexAssign(bool b, const size_t i)  trusted pure 
 nothrow in {
         static assert(i < len);
     } body {
         b ? bts(ptr, i) : btr(ptr, i);
         return b;
     }

 would suffice but then DMD complains as follows

     dmd -debug -gc -gs -unittest -D 
 -Dd/home/per/.emacs.d/auto-builds/dmd/Debug-Boundscheck-Unittest/
ome/per/Work/justd/ 
 -w -main  ~/Work/justd/bitset.d 
 /home/per/Work/justd/assert_ex.d 
 -of/home/per/.emacs.d/auto-builds/dmd/Debug-Boundscheck-Unittest/home/per/Work/justd/bitset
     /home/per/Work/justd/bitset.d(58): Error: 
 bitset.BitSet!2.BitSet.opIndexAssign called with argument types 
 (bool, int) matches both:
     	/home/per/Work/justd/bitset.d(49): opIndexAssign(bool b, 
 ulong i)
     and:
     	/home/per/Work/justd/bitset.d(65): opIndexAssign(bool b, 
 const(ulong) i)
     /home/per/Work/justd/bitset.d(66): Error: variable i cannot 
 be read at compile time
     /home/per/Work/justd/bitset.d(66):        while evaluating: 
 static assert(i < 2LU)
     /home/per/Work/justd/bitset.d(58): Error: 
 bitset.BitSet!2.BitSet.opIndexAssign called with argument types 
 (bool, int) matches both:
     	/home/per/Work/justd/bitset.d(49): opIndexAssign(bool b, 
 ulong i)

 Do I have to make parameter `i` a template parameter, say using 
 type `U`, and then use static if `someTypeTrait!U`. I tried 
 this but isMutable!Index always evaluates to true.

     import std.traits: isIntegral;
     bool opIndexAssign(Index)(bool b, Index i)  trusted pure 
 nothrow if (isIntegral!Index) in {
         import std.traits: isMutable;
         // See also: 
 http://stackoverflow.com/questions/19906516/static-parameter-function-specialization-in-d
         static if (isMutable!Index) {
             assert(i < len);
         } else {
             import std.conv: to;
             static assert(i < len,
                           "Index " ~ to!string(i) ~ " must be 
 smaller than BitSet length " ~  to!string(len));
         }
     } body {
         b ? bts(ptr, i) : btr(ptr, i);
         return b;
     }


It's possible that the compiler can inline the function and 
optimize the code from there, but I don't know of any language 
feature that can do this explicitly.
Nov 11 2013
prev sibling parent reply "Dicebot" <public dicebot.lv> writes:
Please never post such questions to announcement list. There is a 
D.learn for that.
Nov 11 2013
parent reply =?UTF-8?B?Ik5vcmRsw7Z3Ig==?= <per.nordlow gmail.com> writes:
On Monday, 11 November 2013 at 14:41:14 UTC, Dicebot wrote:

 Please never post such questions to announcement list. There is 
 a D.learn for that.


I'm very sorry. It was a mistake. Can I move or delete this post?
Nov 11 2013
next sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
On Monday, November 11, 2013 17:56:38 Nordl=C3=B6w wrote:

 On Monday, 11 November 2013 at 14:41:14 UTC, Dicebot wrote:

 Please never post such questions to announcement list. There is
 a D.learn for that.


=20
 I'm very sorry. It was a mistake. Can I move or delete this post?


No. This forum has three front-ends - nntp newsgroup, mailing list, and=
 the=20
website - with nntp as the backend. So, in general, once it's out there=
, it's=20
out there. Occasionally, Walter will remove spam from the nntp server s=
o that=20
it doesn't end up in the archives, but that's pretty much it. Just be m=
ore=20
careful about where you post in the future.

- Jonathan M Davis
Nov 11 2013
prev sibling parent reply John J <john.joyus gmail.com> writes:
On 11/11/2013 11:56 AM, "Nordlöw" wrote:

 Can I move or delete this post?


I use Thunderbird and it's pretty easy to cancel my own messages:
Just select the post, go to 'Message' menu and click 'Cancel message'

The 'Delete' option is different though, it just deletes the message 
from your local computer while it still exists in the newsgroup for 
others to see.
Nov 12 2013
parent "Dicebot" <public dicebot.lv> writes:
On Tuesday, 12 November 2013 at 22:17:46 UTC, John J wrote:

 On 11/11/2013 11:56 AM, "Nordlöw" wrote:

 Can I move or delete this post?


 I use Thunderbird and it's pretty easy to cancel my own 
 messages:
 Just select the post, go to 'Message' menu and click 'Cancel 
 message'


It will actually send a new message that says that previous one 
should be discarded. Some mail servers / clients can be 
configured to respect that request but I'd be surprised to see 
that for NG.
Nov 12 2013