• tcak (9/9) May 24 2015 Is there any syntax for something like that:
• Jonathan M Davis via Digitalmars-d-learn (17/26) May 24 2015 What about it isn't accepted? This code compiles just fine
• tcak (7/41) May 24 2015 Well, if I do not check the line number of error, this happens.
• Jonathan M Davis via Digitalmars-d-learn (17/65) May 24 2015 shared(FileResourceList) is not implicitly convertible to FileResource. ...
• tcak (6/41) May 24 2015 Nah. Its all about giving the T value on object creation.
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (7/15) May 25 2015 struct and class templates do not have automatic type deduction;
• thedeemon (4/8) May 25 2015 Compiler means "template is used as a type" which is an error

"tcak" <tcak gmail.com> writes:

Is there any syntax for something like that:

class Resource(T) if( is(T: FileResource) ){
}


I tried it as above, but it is not accepted. Maybe I am following 
a wrong syntax.

I tried

class Resource(T: FileResource){
}

But it is not accepted as well.

Jonathan M Davis via Digitalmars-d-learn writes:

On Monday, May 25, 2015 03:19:29 tcak via Digitalmars-d-learn wrote:
 Is there any syntax for something like that:

 class Resource(T) if( is(T: FileResource) ){
 }


 I tried it as above, but it is not accepted. Maybe I am following
 a wrong syntax.

 I tried

 class Resource(T: FileResource){
 }

 But it is not accepted as well.

What about it isn't accepted? This code compiles just fine


class FileResource
{
}

class SubFileResource : FileResource
{
}

class Resource(T)
    if(is(T : FileResource))
{
}

void main()
{
    Resource!SubFileResource foo;
}

- Jonathan M Davis

"tcak" <tcak gmail.com> writes:

On Monday, 25 May 2015 at 03:35:22 UTC, Jonathan M Davis wrote:
 On Monday, May 25, 2015 03:19:29 tcak via Digitalmars-d-learn 
 wrote:
 Is there any syntax for something like that:

 class Resource(T) if( is(T: FileResource) ){
 }


 I tried it as above, but it is not accepted. Maybe I am 
 following
 a wrong syntax.

 I tried

 class Resource(T: FileResource){
 }

 But it is not accepted as well.

 What about it isn't accepted? This code compiles just fine


 class FileResource
 {
 }

 class SubFileResource : FileResource
 {
 }

 class Resource(T)
     if(is(T : FileResource))
 {
 }

 void main()
 {
     Resource!SubFileResource foo;
 }

 - Jonathan M Davis

Well, if I do not check the line number of error, this happens. 
It was giving error on the line of creating a new instance.

Line 243: auto fileResourceList = new shared FileResourceList( 2 
);

main.d(243): Error: class main.FileResourceList(T) if (is(T : 
FileResource)) is used as a type

Jonathan M Davis via Digitalmars-d-learn writes:

On Monday, May 25, 2015 03:42:22 tcak via Digitalmars-d-learn wrote:
 On Monday, 25 May 2015 at 03:35:22 UTC, Jonathan M Davis wrote:
 On Monday, May 25, 2015 03:19:29 tcak via Digitalmars-d-learn
 wrote:
 Is there any syntax for something like that:

 class Resource(T) if( is(T: FileResource) ){
 }


 I tried it as above, but it is not accepted. Maybe I am
 following
 a wrong syntax.

 I tried

 class Resource(T: FileResource){
 }

 But it is not accepted as well.

 What about it isn't accepted? This code compiles just fine


 class FileResource
 {
 }

 class SubFileResource : FileResource
 {
 }

 class Resource(T)
     if(is(T : FileResource))
 {
 }

 void main()
 {
     Resource!SubFileResource foo;
 }

 - Jonathan M Davis

 Well, if I do not check the line number of error, this happens.
 It was giving error on the line of creating a new instance.

 Line 243: auto fileResourceList = new shared FileResourceList( 2
 );

 main.d(243): Error: class main.FileResourceList(T) if (is(T :
 FileResource)) is used as a type

shared(FileResourceList) is not implicitly convertible to FileResource. It
may be implicitly convertible to shared(FileResource), but not
FileResource). Code that uses shared usually has to be written specifically
for shared. Also, any time that you construct a templated type, you have to
provide the template argument. IFTI (implicit function template
instantiation) doesn't work with constructors. To make that work, you need a
wrapper function - e.g.

auto resource(T)(T t)
{
    return new Resource!T(t);
}

So, I suspect that you're either running into problems, because you're using
shared, and Resource's template constraint requires non-shared, and/or
because you aren't explicitly instantiating Resource with a template
argument.

- Jonathan M Davis

"tcak" <tcak gmail.com> writes:

On Monday, 25 May 2015 at 04:07:06 UTC, Jonathan M Davis wrote:
 On Monday, May 25, 2015 03:42:22 tcak via Digitalmars-d-learn 
 wrote:
 Well, if I do not check the line number of error, this happens.
 It was giving error on the line of creating a new instance.

 Line 243: auto fileResourceList = new shared FileResourceList( 
 2
 );

 main.d(243): Error: class main.FileResourceList(T) if (is(T :
 FileResource)) is used as a type

 shared(FileResourceList) is not implicitly convertible to 
 FileResource. It
 may be implicitly convertible to shared(FileResource), but not
 FileResource). Code that uses shared usually has to be written 
 specifically
 for shared. Also, any time that you construct a templated type, 
 you have to
 provide the template argument. IFTI (implicit function template
 instantiation) doesn't work with constructors. To make that 
 work, you need a
 wrapper function - e.g.

 auto resource(T)(T t)
 {
     return new Resource!T(t);
 }

 So, I suspect that you're either running into problems, because 
 you're using
 shared, and Resource's template constraint requires non-shared, 
 and/or
 because you aren't explicitly instantiating Resource with a 
 template
 argument.

 - Jonathan M Davis

Nah. Its all about giving the T value on object creation.

auto fileResourceList = new shared FileResourceList!FileResource( 
2 );

Then it works. The error message is not indicating directly this, 
though logically it is still correct.

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 05/24/2015 09:14 PM, tcak wrote:

 Line 243: auto fileResourceList = new shared FileResourceList( 2
 );

 main.d(243): Error: class main.FileResourceList(T) if (is(T :
 FileResource)) is used as a type



struct and class templates do not have automatic type deduction; 
function templates do. The solution is to provide a convenience function 
template alongside the struct or class.

 auto fileResourceList = new shared FileResourceList!FileResource( 2 );

 Then it works. The error message is not indicating directly this, though
 logically it is still correct.

'if (is(T : FileResource))' part means "if T can implicitly be converted 
to FileResource". You still provide T so that it gets checked.

Ali

"thedeemon" <dlang thedeemon.com> writes:

On Monday, 25 May 2015 at 04:15:00 UTC, tcak wrote:

 main.d(243): Error: class main.FileResourceList(T) if (is(T :
 FileResource)) is used as a type



 The error message is not indicating directly this, though 
 logically it is still correct.

Compiler means "template is used as a type" which is an error 
since templates are not types. I guess adding the word "template" 
to that message would make it more clear.