www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - class template as a type

reply Karl <asdf asdf.com> writes:
Hi,

I've been playing around with templates, i'm a newbie in this matter, i created
a class template and i want to use it as a type in functions and create arrays
of it. Any help please.

Code sample:

module hello;

template Test(alias T)
{
    class Test
    {
        this(){} int x; ...
    }
}

void Foo(Test t){}

static Test[] myarray;
Sep 18 2007
parent reply BCS <ao pathlink.com> writes:
Reply to Karl,


 Hi,
 
 I've been playing around with templates, i'm a newbie in this matter,
 i created a class template and i want to use it as a type in functions
 and create arrays of it. Any help please.
 
 Code sample:
 
 module hello;
 
 template Test(alias T)
 {
 class Test
 {
 this(){} int x; ...
 }
 }
 void Foo(Test t){}
 
 static Test[] myarray;
 



void Foo(Test!(somthingToAlias) { }
static Test!(somthingToAlias)[] myarray;

look for "Explicit Template Instantiation" in

http://www.digitalmars.com/d/template.html
Sep 18 2007
parent reply Karl <asdf asdf.com> writes:
BCS Wrote:


 Reply to Karl,
 

 Hi,
 
 I've been playing around with templates, i'm a newbie in this matter,
 i created a class template and i want to use it as a type in functions
 and create arrays of it. Any help please.
 
 Code sample:
 
 module hello;
 
 template Test(alias T)
 {
 class Test
 {
 this(){} int x; ...
 }
 }
 void Foo(Test t){}
 
 static Test[] myarray;
 



 void Foo(Test!(somthingToAlias) { }
 static Test!(somthingToAlias)[] myarray;
 
 look for "Explicit Template Instantiation" in
 
 http://www.digitalmars.com/d/template.html
 
 



Thanks for your reply.

"somthingToAlias" could be anything right? Lets suppose foo.bar1 or foo.bar2.
Then "static Test!(foo.bar1)[] myarray;" would create an array only for
elements instantiated from foo.bar1 and i couldn't append an element
instantiated from foo.bar2, am i wrong?

1) Then how could i create an array for generic instantiated elements?

2) "void Foo(Test!(somthingToAlias) { }", i think something is missing:

- ")".
- A variable name, (correct me if wrong): void Foo(Test!(somthingToAlias) 
sta){ }

Thanks in advance.
Sep 18 2007
parent reply Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
Karl wrote:

 BCS Wrote:
 

 void Foo(Test!(somthingToAlias) { }
 static Test!(somthingToAlias)[] myarray;

 look for "Explicit Template Instantiation" in

 http://www.digitalmars.com/d/template.html



 "somthingToAlias" could be anything right? Lets suppose foo.bar1 or foo.bar2.
Then "static Test!(foo.bar1)[] myarray;" would create an array only for
elements instantiated from foo.bar1 and i couldn't append an element
instantiated from foo.bar2, am i wrong?
 
 1) Then how could i create an array for generic instantiated elements?



You could give your template class a non-templated base function, and 
use that as the type of the array elements.


 2) "void Foo(Test!(somthingToAlias) { }", i think something is missing:
 
 - ")".



Yes, he seems to have made a typo there


 - A variable name, (correct me if wrong): void Foo(Test!(somthingToAlias) 
sta){ }



Technically the name is optional, but it does come in quite handy when 
you actually want to *use* the parameter in the function body :).
Sep 19 2007
parent reply Karl <asdf asdf.com> writes:
Frits van Bommel Wrote:


 Karl wrote:

 BCS Wrote:
 

 void Foo(Test!(somthingToAlias) { }
 static Test!(somthingToAlias)[] myarray;

 look for "Explicit Template Instantiation" in

 http://www.digitalmars.com/d/template.html



 "somthingToAlias" could be anything right? Lets suppose foo.bar1 or foo.bar2.
Then "static Test!(foo.bar1)[] myarray;" would create an array only for
elements instantiated from foo.bar1 and i couldn't append an element
instantiated from foo.bar2, am i wrong?
 
 1) Then how could i create an array for generic instantiated elements?



 You could give your template class a non-templated base function, and 
 use that as the type of the array elements.
 

 2) "void Foo(Test!(somthingToAlias) { }", i think something is missing:
 
 - ")".



 Yes, he seems to have made a typo there
 

 - A variable name, (correct me if wrong): void Foo(Test!(somthingToAlias) 
sta){ }



 Technically the name is optional, but it does come in quite handy when 
 you actually want to *use* the parameter in the function body :).



Thanks for your reply.

"You could give your template class a non-templated base function, and 
use that as the type of the array elements."

I didn't understood. A small example please.

Thanks man.
Sep 19 2007
parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Karl" <asdf asdf.com> wrote in message 
news:fcsokc$2uhn$1 digitalmars.com...


 "You could give your template class a non-templated base function, and
 use that as the type of the array elements."

 I didn't understood. A small example please.



He meant "non-templated base *class*".  So:

class TestBase
{
    // put common methods here
}

class Test(alias T) : TestBase
{
    this()
    {

    }

    int x;

    ...
}

void Foo(TestBase t) {}
static TestBase[] myArray;

Remember that unlike Java or C# generics, D's templates are done all at 
compile time.  This means that a Test!(int) is just as different from a 
Test!(float) as an int[] is from a float[].
Sep 19 2007
parent reply Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
Jarrett Billingsley wrote:

 "Karl" <asdf asdf.com> wrote in message 
 news:fcsokc$2uhn$1 digitalmars.com...
 

 "You could give your template class a non-templated base function, and
 use that as the type of the array elements."

 I didn't understood. A small example please.



 He meant "non-templated base *class*".  So:



Yes I did. I'm not quite sure how I managed to typo 'class' to 
'function' though...
Sep 19 2007
parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Frits van Bommel" <fvbommel REMwOVExCAPSs.nl> wrote in message 
news:fct4r0$hl9$1 digitalmars.com...

 Yes I did. I'm not quite sure how I managed to typo 'class' to 'function' 
 though...



It's understandable.  The keys are right next to each other.
Sep 20 2007
parent Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
Jarrett Billingsley wrote:

 "Frits van Bommel" <fvbommel REMwOVExCAPSs.nl> wrote in message 
 news:fct4r0$hl9$1 digitalmars.com...

 Yes I did. I'm not quite sure how I managed to typo 'class' to 'function' 
 though...



 It's understandable.  The keys are right next to each other. 
 
 



You have a [class] key on your keyboard!?  ...is that thing available on Amazon?

-- Chris Nicholson-Sauls
Sep 20 2007