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digitalmars.D - Is this is bug or not?

reply Victor Nakoryakov <Victor_member pathlink.com> writes:
Hi all,

Here is a snipet:

import std.stdio;

struct A(T, T x0)
{
T x = x0;
}

int main(char[][] args)
{
alias A!(int, 8) Ai; // test.d(11)
Ai ai;
writefln(ai.x);
return 0;
}

DMD output is:
test.d(11): template instance A!(int,8) does not match any template declaration

However snipet:

import std.stdio;

struct A(T, int x0) // note int instead of T
{
T x = x0;
}

int main(char[][] args)
{
alias A!(int, 8) Ai;
Ai ai;
writefln(ai.x);
return 0;
}

works as expected. Is former is a templates issue or bug?

--
Victor Nakoryakov (aka nail)
nail-mail[at]mail.ru

Krasnoznamensk, Moscow, Russia
Mar 11 2006
parent reply Thomas Kuehne <thomas-dloop kuehne.cn> writes:
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Hash: SHA1

Victor Nakoryakov schrieb am 2006-03-11:

 Hi all,

 Here is a snipet:

 import std.stdio;

 struct A(T, T x0)
 {
 T x = x0;
 }

 int main(char[][] args)
 {
 alias A!(int, 8) Ai; // test.d(11)
 Ai ai;
 writefln(ai.x);
 return 0;
 }

 DMD output is:
 test.d(11): template instance A!(int,8) does not match any template declaration

 However snipet:

 import std.stdio;

 struct A(T, int x0) // note int instead of T
 {
 T x = x0;
 }

 int main(char[][] args)
 {
 alias A!(int, 8) Ai;
 Ai ai;
 writefln(ai.x);
 return 0;
 }

 works as expected. Is former is a templates issue or bug?


Added to DStress as
http://dstress.kuehne.cn/run/t/template_31_A.d
http://dstress.kuehne.cn/run/t/template_31_B.d
http://dstress.kuehne.cn/run/t/template_31_C.d
http://dstress.kuehne.cn/run/t/template_31_D.d

template_31_C seems funny, but I'm not aware of any statement against
it.

Thomas


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Mar 15 2006
parent reply Don Clugston <dac nospam.com.au> writes:
Thomas Kuehne wrote:

 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
 Victor Nakoryakov schrieb am 2006-03-11:

 Hi all,

 Here is a snipet:

 import std.stdio;

 struct A(T, T x0)
 {
 T x = x0;
 }

 int main(char[][] args)
 {
 alias A!(int, 8) Ai; // test.d(11)
 Ai ai;
 writefln(ai.x);
 return 0;
 }




If that had worked, it would have been a new feature. You're obtaining a 
type AND a value! Note that value parameters only work for basic types 
and char[]. It would be very cool, though -- it would enable a lot of 
code reuse for metaprogramming.

For example, pow!(real z, int n) and pow!(creal z, int n) would be able 
to share a common implementation. The fact that they can't has been 
bugging me for some time.
Mar 17 2006
parent Sean Kelly <sean f4.ca> writes:
Don Clugston wrote:

 Thomas Kuehne wrote:

 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1

 Victor Nakoryakov schrieb am 2006-03-11:

 Hi all,

 Here is a snipet:

 import std.stdio;

 struct A(T, T x0)
 {
 T x = x0;
 }

 int main(char[][] args)
 {
 alias A!(int, 8) Ai; // test.d(11)
 Ai ai;
 writefln(ai.x);
 return 0;
 }




 
 If that had worked, it would have been a new feature. You're obtaining a 
 type AND a value! Note that value parameters only work for basic types 
 and char[]. It would be very cool, though -- it would enable a lot of 
 code reuse for metaprogramming.
 
 For example, pow!(real z, int n) and pow!(creal z, int n) would be able 
 to share a common implementation. The fact that they can't has been 
 bugging me for some time.


For what it's worth, this is legal in C++:

     #include <iostream>

     template<class T, T x>
     struct S
     {
         static const T val = x;
     };

     int main()
     {
         int x = S<int,5>::val;
         std::cout << x << '\n';
     }

Sean
Mar 17 2006