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digitalmars.D.learn - Pointer to template types?

reply "Chris" <wendlec tcd.ie> writes:
I need an array that contains pointers to types created via 
template. To stick to my usual example:

Person!(string)

How can I make an array with pointers to concrete "instances" of 
Person!(string)?

Something like this only with pointers, i.e. buf holds pointers 
to concrete Person!(string)s:

Appender!(Person!(string)[]) buf = appender!(Person!(string)[]);

Thanks in advance.
Apr 28 2014
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Chris:


 I need an array that contains pointers to types created via 
 template. To stick to my usual example:

 Person!(string)

 How can I make an array with pointers to concrete "instances" 
 of Person!(string)?


Every template creates a new type, so you can't put them as they 
are in an array. There are various solutions, none nice. You can 
try with a wrapper that performs type erasure, or simpler you can 
make all the same type giving them the string at run-time. 
Another solution is use OOP, something like (untested and I am 
not sure):

abstract class APerson {}
class Person(string name) : APerson {}

Bye,
bearophile
Apr 28 2014
next sibling parent "Chris" <wendlec tcd.ie> writes:
On Monday, 28 April 2014 at 10:32:18 UTC, bearophile wrote:

 Chris:


 I need an array that contains pointers to types created via 
 template. To stick to my usual example:

 Person!(string)

 How can I make an array with pointers to concrete "instances" 
 of Person!(string)?


 Every template creates a new type, so you can't put them as 
 they are in an array. There are various solutions, none nice. 
 You can try with a wrapper that performs type erasure, or 
 simpler you can make all the same type giving them the string 
 at run-time. Another solution is use OOP, something like 
 (untested and I am not sure):

 abstract class APerson {}
 class Person(string name) : APerson {}

 Bye,
 bearophile


So there is no way of filling an array with something like

Person!(string) *pptr;

foreach(person; people) {
   buf ~= &person;
}
Apr 28 2014
prev sibling parent reply "Chris" <wendlec tcd.ie> writes:
On Monday, 28 April 2014 at 10:32:18 UTC, bearophile wrote:

 Chris:


 I need an array that contains pointers to types created via 
 template. To stick to my usual example:

 Person!(string)

 How can I make an array with pointers to concrete "instances" 
 of Person!(string)?


 Every template creates a new type, so you can't put them as 
 they are in an array. There are various solutions, none nice. 
 You can try with a wrapper that performs type erasure, or 
 simpler you can make all the same type giving them the string 
 at run-time. Another solution is use OOP, something like 
 (untested and I am not sure):

 abstract class APerson {}
 class Person(string name) : APerson {}

 Bye,
 bearophile


So there is no way of filling an array with something like

Person!(string) *pptr;

foreach(person; people) {
    buf ~= &person;
}
Apr 28 2014
next sibling parent reply "Rene Zwanenburg" <renezwanenburg gmail.com> writes:
On Monday, 28 April 2014 at 10:40:49 UTC, Chris wrote:

 So there is no way of filling an array with something like

 Person!(string) *pptr;

 foreach(person; people) {
    buf ~= &person;
 }


Person!(string)*[] arr;

Like this?
Apr 28 2014
parent "Chris" <wendlec tcd.ie> writes:
On Monday, 28 April 2014 at 10:44:18 UTC, Rene Zwanenburg wrote:

 On Monday, 28 April 2014 at 10:40:49 UTC, Chris wrote:

 So there is no way of filling an array with something like

 Person!(string) *pptr;

 foreach(person; people) {
   buf ~= &person;
 }


 Person!(string)*[] arr;

 Like this?


Exactly, just tried it, this works. I tried various types of 
syntax and just couldn't get it right. Thanks a million.
Apr 28 2014
prev sibling next sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Chris:


 So there is no way of filling an array with something like

 Person!(string) *pptr;

 foreach(person; people) {
    buf ~= &person;
 }


So you want an array filled with instances of the same 
instantiation, sorry, I misunderstood your problem for a more 
complex one :-)

Bye,
bearophile
Apr 28 2014
parent "Chris" <wendlec tcd.ie> writes:
On Monday, 28 April 2014 at 11:04:17 UTC, bearophile wrote:

 Chris:


 So there is no way of filling an array with something like

 Person!(string) *pptr;

 foreach(person; people) {
   buf ~= &person;
 }


 So you want an array filled with instances of the same 
 instantiation, sorry, I misunderstood your problem for a more 
 complex one :-)

 Bye,
 bearophile


No worries. I didn't make it clear either that it was about 
syntax.
Apr 28 2014
prev sibling parent reply "Jesse Phillips" <Jesse.K.Phillips+D gmail.com> writes:
On Monday, 28 April 2014 at 10:40:49 UTC, Chris wrote:

 Person!(string) *pptr;


Just wanted to point out, the above is C style and not 
recommended.

     Person!(string)* pptr, pptr2, pptr3;

In D the pointer is part of the type not the variable (all three 
are pointers, unlike C where only the first would be a pointer). 
By placing the pointer on the variable I do not describe the 
types correctly.

     Person!(string) *pptr, pptr2, pptr3;

This should help when wanting to use more complex types:

     Person!(string)*[string][][char]* paaaaapp; //:)

used like :(I don't know my precedence):

     *((*paaaaapp)['c'][1]["hello"])
Apr 28 2014
parent "Chris" <wendlec tcd.ie> writes:
On Tuesday, 29 April 2014 at 04:44:39 UTC, Jesse Phillips wrote:

 On Monday, 28 April 2014 at 10:40:49 UTC, Chris wrote:

 Person!(string) *pptr;


 Just wanted to point out, the above is C style and not 
 recommended.

     Person!(string)* pptr, pptr2, pptr3;

 In D the pointer is part of the type not the variable (all 
 three are pointers, unlike C where only the first would be a 
 pointer). By placing the pointer on the variable I do not 
 describe the types correctly.

     Person!(string) *pptr, pptr2, pptr3;

 This should help when wanting to use more complex types:

     Person!(string)*[string][][char]* paaaaapp; //:)

 used like :(I don't know my precedence):

     *((*paaaaapp)['c'][1]["hello"])


Yes, you're right. Thanks for pointing this out. To be sure, I 
usually use a new line for pointers.
Apr 29 2014