I'm new to D and am playing with D2.0.  When I try to compile the example on http://www.digitalmars.com/d/2.0/mixin.html, I get a compiler error:

--------------------------------------------------------------
template GenStruct(char[] Name, char[] M1)
{
    const char[] GenStruct = "struct " ~ Name ~ "{ int " ~ M1 ~ "; }";
}

mixin(GenStruct!("Foo", "bar"));
--------------------------------------------------------------
testmixin.d(6): template instance GenStruct!("Foo","bar") does not match any template declaration
attribute argument to mixin must be a string, not (GetStruct!("Foo","bar"))
--------------------------------------------------------------

Is there something else needed?

-- Brian

On Thu, 06 Mar 2008 12:02:24 +0100, Brian White <bcwhite@pobox.com> wrote:

> I'm new to D and am playing with D2.0.  When I try to compile the example on http://www.digitalmars.com/d/2.0/mixin.html, I get a compiler error:
>
> --------------------------------------------------------------
> template GenStruct(char[] Name, char[] M1)
> {
>      const char[] GenStruct = "struct " ~ Name ~ "{ int " ~ M1 ~ "; }";
> }
>
> mixin(GenStruct!("Foo", "bar"));
> --------------------------------------------------------------
> testmixin.d(6): template instance GenStruct!("Foo","bar") does not match any template declaration
> attribute argument to mixin must be a string, not (GetStruct!("Foo","bar"))
> --------------------------------------------------------------
>
> Is there something else needed?
>
> -- Brian


The problem is that "Foo" and "bar", as D strings, are invariant(char)[], not char[].

The solution is to change the template to

> template GenStruct(const char[] Name, const char[] M1)

-- Simen

> The problem is that "Foo" and "bar", as D strings, are invariant(char)[], not char[].
> 
> The solution is to change the template to
> 
>> template GenStruct(const char[] Name, const char[] M1)

Got it.  Why not declare them "invariant char[]", or does it simply make no difference?

-- Brian

On Thu, 06 Mar 2008 13:32:57 +0100, Brian White <bcwhite@pobox.com> wrote:

>> The problem is that "Foo" and "bar", as D strings, are invariant(char)[], not char[].
>>  The solution is to change the template to
>>
>>> template GenStruct(const char[] Name, const char[] M1)
>
> Got it.  Why not declare them "invariant char[]", or does it simply make no difference?
>
> -- Brian

Both char[] and invariant(char)[] are implicitly castable to const(char)[]. Had you for some reason done something like this:

template GenStruct(const char[] Name, const char[] M1)
{
  //stuffs
}

char[] myString1 = "Foo";
char[] myString2 = "bar";

GenStruct!(myString1, myString2); // error here, char[] not implicitly castable to invariant(char)[]

-- Simen

Simen Kjaeraas wrote:
> On Thu, 06 Mar 2008 12:02:24 +0100, Brian White <bcwhite@pobox.com> wrote:
> 
>> I'm new to D and am playing with D2.0.  When I try to compile the example on http://www.digitalmars.com/d/2.0/mixin.html, I get a compiler error:
>>
>> --------------------------------------------------------------
>> template GenStruct(char[] Name, char[] M1)
>> {
>>      const char[] GenStruct = "struct " ~ Name ~ "{ int " ~ M1 ~ "; }";
>> }
>>
>> mixin(GenStruct!("Foo", "bar"));
>> --------------------------------------------------------------
>> testmixin.d(6): template instance GenStruct!("Foo","bar") does not match any template declaration
>> attribute argument to mixin must be a string, not (GetStruct!("Foo","bar"))
>> --------------------------------------------------------------
>>
>> Is there something else needed?
>>
>> -- Brian
> 
> 
> The problem is that "Foo" and "bar", as D strings, are invariant(char)[], not char[].
> 
> The solution is to change the template to
> 
>> template GenStruct(const char[] Name, const char[] M1)

You can also use 'string' instead.

   template GenStruct(string Name, string M1)

which is an alias for invariant(char)[] in D2.

--bb