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digitalmars.D - Value-parameters in templates (Bug?)

reply Daniel Keep <daniel.keep dummy.gmail.com> writes:
I think I might have found a(nother) bug :P

#  5
#  6 template strCatMix(char[] S = " ")
#  7 {
#  8     char[] strCatMix(char[] lhs, char[] rhs)
#  9     {
# 10         return lhs ~ S ~ rhs;
# 11     }
# 12 }
# 13

Compiling this with w/ dmd, I get:

listtest.d(6): Error: integral type expected for value-parameter, not char[]

As far as I can tell from the D website, this should be perfectly fine, 
as it doesn't mention anywhere that the value-parameter must be an int. 
  Is the documentation just ambiguous, or is this not yet finished in 
the compiler?

	-- Daniel
Nov 17 2004
next sibling parent reply "Simon Buchan" <currently no.where> writes:
On Thu, 18 Nov 2004 00:50:34 +1100, Daniel Keep  
<daniel.keep dummy.gmail.com> wrote:


 I think I might have found a(nother) bug :P

 #  5
 #  6 template strCatMix(char[] S = " ")
 #  7 {
 #  8     char[] strCatMix(char[] lhs, char[] rhs)
 #  9     {
 # 10         return lhs ~ S ~ rhs;
 # 11     }
 # 12 }
 # 13

 Compiling this with w/ dmd, I get:

 listtest.d(6): Error: integral type expected for value-parameter, not  
 char[]

 As far as I can tell from the D website, this should be perfectly fine,  
 as it doesn't mention anywhere that the value-parameter must be an int.  
   Is the documentation just ambiguous, or is this not yet finished in  
 the compiler?

 	-- Daniel



I suspect dmd is expecting only one argument for the function strCatMix(),
as you only gave one for the template. How are you expecting to use this?
I dont know where dmd gets all its ints from, unfortunatly.

-- 
Using Opera's revolutionary e-mail client: http://www.opera.com/m2/
Nov 17 2004
parent reply Daniel Keep <daniel.keep dummy.gmail.com> writes:
Well, it doesn't make any difference if I change the name of the 
function/template.  Basically, it's for a functional library I'm toying 
with.  It's used like this:

alias strCatMix!(", ")		StrCatComma;
stdout.writeLine("["~StrReduce(&StrCatComma, someListOfStrings)~"]");

Or something like that :P  As near as I can see, the number of 
parameters for the template doesn't have any bearing on the number of 
parameters in the function.

	-- Daniel

Simon Buchan wrote:

 On Thu, 18 Nov 2004 00:50:34 +1100, Daniel Keep  
 <daniel.keep dummy.gmail.com> wrote:
 

 I think I might have found a(nother) bug :P

 #  5
 #  6 template strCatMix(char[] S = " ")
 #  7 {
 #  8     char[] strCatMix(char[] lhs, char[] rhs)
 #  9     {
 # 10         return lhs ~ S ~ rhs;
 # 11     }
 # 12 }
 # 13

 Compiling this with w/ dmd, I get:

 listtest.d(6): Error: integral type expected for value-parameter, not  
 char[]

 As far as I can tell from the D website, this should be perfectly 
 fine,  as it doesn't mention anywhere that the value-parameter must be 
 an int.    Is the documentation just ambiguous, or is this not yet 
 finished in  the compiler?

     -- Daniel



 
 I suspect dmd is expecting only one argument for the function strCatMix(),
 as you only gave one for the template. How are you expecting to use this?
 I dont know where dmd gets all its ints from, unfortunatly.
Nov 17 2004
next sibling parent "Simon Buchan" <currently no.where> writes:
On Thu, 18 Nov 2004 01:16:04 +1100, Daniel Keep  
<daniel.keep dummy.gmail.com> wrote:

I think this is your problem: (from  
http://www.digitalmars.com/d/index.html, frame  
http://www.digitalmars.com/d/template.html)

Implicit Template Properties
If a template has exactly one member in it, and the name of that member is  
the same as the template name, that member is assumed to be referred to in  
a template instantiation:

template Foo(T)
{
     T Foo;// declare variable Foo of type T
}

void test()
{
     Foo!(int) = 6;// instead of Foo!(int).Foo
}

Haven't any idea what using & on a template instance would do...


 Well, it doesn't make any difference if I change the name of the  
 function/template.  Basically, it's for a functional library I'm toying  
 with.  It's used like this:

 alias strCatMix!(", ")		StrCatComma;
 stdout.writeLine("["~StrReduce(&StrCatComma, someListOfStrings)~"]");

 Or something like that :P  As near as I can see, the number of  
 parameters for the template doesn't have any bearing on the number of  
 parameters in the function.

 	-- Daniel

 Simon Buchan wrote:

 On Thu, 18 Nov 2004 00:50:34 +1100, Daniel Keep   
 <daniel.keep dummy.gmail.com> wrote:


 I think I might have found a(nother) bug :P

 #  5
 #  6 template strCatMix(char[] S = " ")
 #  7 {
 #  8     char[] strCatMix(char[] lhs, char[] rhs)
 #  9     {
 # 10         return lhs ~ S ~ rhs;
 # 11     }
 # 12 }
 # 13

 Compiling this with w/ dmd, I get:

 listtest.d(6): Error: integral type expected for value-parameter, not   
 char[]

 As far as I can tell from the D website, this should be perfectly  
 fine,  as it doesn't mention anywhere that the value-parameter must be  
 an int.    Is the documentation just ambiguous, or is this not yet  
 finished in  the compiler?

     -- Daniel



 strCatMix(),
 as you only gave one for the template. How are you expecting to use  
 this?
 I dont know where dmd gets all its ints from, unfortunatly.








-- 
Using Opera's revolutionary e-mail client: http://www.opera.com/m2/
Nov 17 2004
prev sibling parent Regan Heath <regan netwin.co.nz> writes:
On Thu, 18 Nov 2004 01:16:04 +1100, Daniel Keep 
<daniel.keep dummy.gmail.com> wrote:

 Well, it doesn't make any difference if I change the name of the 
 function/template.  Basically, it's for a functional library I'm toying 
 with.  It's used like this:

 alias strCatMix!(", ")		StrCatComma;
 stdout.writeLine("["~StrReduce(&StrCatComma, someListOfStrings)~"]");

 Or something like that :P  As near as I can see, the number of 
 parameters for the template doesn't have any bearing on the number of 
 parameters in the function.



Try this:

import std.stdio;

template test(T:T[],alias S) {
   char[] foo(T[] a, T[] b) {
     return a ~ S ~ b;
   }
}

char[] comma = ", ";
alias test!(char[],comma).foo catComma;

void main()
{
	char[] a = "Heath";
	char[] b = "Regan";
	
	writef(catComma(a,b));
}

Regan
Nov 17 2004
prev sibling next sibling parent reply "Lionello Lunesu" <lionello.lunesu crystalinter.remove.com> writes:
 #  6 template strCatMix(char[] S = " ")



Hi there.
Never wrote a D program in my life, but I've noticed that char[] is actually 
an array, so it's certainly not a "single value".

What happens if you write (char* S =" "), then it's a value. D supports 
C-style pointers, right?

Lionello.
Nov 17 2004
parent Regan Heath <regan netwin.co.nz> writes:
On Wed, 17 Nov 2004 16:11:58 +0200, Lionello Lunesu 
<lionello.lunesu crystalinter.remove.com> wrote:

 #  6 template strCatMix(char[] S = " ")



 Hi there.
 Never wrote a D program in my life, but I've noticed that char[] is 
 actually
 an array, so it's certainly not a "single value".

 What happens if you write (char* S =" "), then it's a value. D supports
 C-style pointers, right?



Yes, but..

import std.stdio;

template test(char *S = ", ") {
   char[] foo(char[] a, char[] b) {
     return a ~ S ~ b;
   }
}

alias test!().foo catComma;

void main()
{
	char[] a = "Heath";
	char[] b = "Regan";
	
	writef(catComma(a,b));
}

strcat.d(3): Error: integral type expected for value-parameter, not char*

apparently 'char *' is not an integral type.

Regan

-- 
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/
Nov 17 2004
prev sibling next sibling parent Nick <Nick_member pathlink.com> writes:
In article <cnfkpe$ud3$1 digitaldaemon.com>, Daniel Keep says...

[...]
listtest.d(6): Error: integral type expected for value-parameter, not char[]

As far as I can tell from the D website, this should be perfectly fine, 
as it doesn't mention anywhere that the value-parameter must be an int. 
  Is the documentation just ambiguous, or is this not yet finished in 
the compiler?



It's hard to tell. The docs do not mention anything about it, but all the given
examples are ints. I also hope there will be support for other types in the
future, since there doesn't seem to be any clear reason why value parameters
should be restricted to integers.

Here is the test case I used:

# import std.stdio;
#
# template hello(char[] s)
# {
#   void hello() { writefln(s); }
# }
#
# void main()
# {
#   hello!("Hello World!");
# }

It gives exactly the same error that you got.

Nick
Nov 17 2004
prev sibling next sibling parent Sean Kelly <sean f4.ca> writes:
In article <cnfkpe$ud3$1 digitaldaemon.com>, Daniel Keep says...

I think I might have found a(nother) bug :P

#  5
#  6 template strCatMix(char[] S = " ")
#  7 {
#  8     char[] strCatMix(char[] lhs, char[] rhs)
#  9     {
# 10         return lhs ~ S ~ rhs;
# 11     }
# 12 }
# 13

Compiling this with w/ dmd, I get:

listtest.d(6): Error: integral type expected for value-parameter, not char[]

As far as I can tell from the D website, this should be perfectly fine, 
as it doesn't mention anywhere that the value-parameter must be an int. 
  Is the documentation just ambiguous, or is this not yet finished in 
the compiler?



This is correct behavior.  Since templates are evaluated at compile-time, you
need to provide something that can be evaluated at compile-time such as an
integer constant, etc.  C++ allows you to use static arrays as template
parameters like so:

# template<char* T>
# class C
# {
#     char* val;
# public:
#     C() : val(T) {}
# };
# 
# char x[] = "hi";
# 
# C<x> c;

But D does not allow this.  Instead you need to use an alias parameter:

# template t(alias T)
# {
#     alias T val;
# }
# 
# static char[] x = "hi";
# 
# void main()
# {
#     printf( "%.*s\n", t!(x).val );
# }

Note that this is functionally the same as the C++ approach, as the char array
must be a static global variable.


Sean
Nov 17 2004
prev sibling parent "Carlos Santander B." <carlos8294 msn.com> writes:
"Daniel Keep" <daniel.keep dummy.gmail.com> escribió en el mensaje 
news:cnfkpe$ud3$1 digitaldaemon.com...
|I think I might have found a(nother) bug :P
|
| #  5
| #  6 template strCatMix(char[] S = " ")
| #  7 {
| #  8     char[] strCatMix(char[] lhs, char[] rhs)
| #  9     {
| # 10         return lhs ~ S ~ rhs;
| # 11     }
| # 12 }
| # 13
|
| Compiling this with w/ dmd, I get:
|
| listtest.d(6): Error: integral type expected for value-parameter, not char[]
|
| As far as I can tell from the D website, this should be perfectly fine,
| as it doesn't mention anywhere that the value-parameter must be an int.
|  Is the documentation just ambiguous, or is this not yet finished in
| the compiler?
|
| -- Daniel

From template.html (a couple of paragraphs below the grammar specification):

"Template parameters can be types, values, or symbols. Types can be any type. 
Value parameters must be of an integral type, and specializations for them must 
resolve to an integral constant. Symbols can be any non-local symbol."

-----------------------
Carlos Santander Bernal
Nov 17 2004