• Claude (32/32) Dec 30 2014 Hello, I'm trying to use templates to define several methods
• Steven Schveighoffer (14/40) Dec 30 2014 I think it has to do with the fact that when you are defining the
• Steven Schveighoffer (10/22) Dec 30 2014 A possibly more elegant solution, use opDispatch:
• Daniel =?UTF-8?B?S296w6Fr?= via Digitalmars-d-learn (29/69) Dec 30 2014 V Tue, 30 Dec 2014 13:17:08 +0000
• Claude (8/17) Dec 30 2014 I tested both the "string mixin" and "opAssign" implementations,
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (5/7) Dec 30 2014 I just saw this post, which is essentially the same question as Basile
• Claude (8/11) Jan 08 2015 Maybe using templates to create properties is a bit overkill in

"Claude" <claudemr live.fr> writes:

Hello, I'm trying to use templates to define several methods 
(property setters) within a class to avoid some code duplication.
Here is an attempt:

class Camera
{
private:
     Vector4 m_pos;
     float m_fov, m_ratio, m_near, m_far;
     bool m_matrixCalculated;

public:
     void SetProperty(Tin, alias Field)(ref Tin param)  property 
pure  safe
     {
         Field = param;
         m_matrixCalculated = false;
     }

     alias pos   = SetProperty!(float[], m_pos);
     alias pos   = SetProperty!(Vector4, m_pos);
     alias ratio = SetProperty!(float,   m_ratio);
     alias near  = SetProperty!(float,   m_near);
     alias far   = SetProperty!(float,   m_far);
}

I get this kind of compilation error:
Error: template instance SetProperty!(float[], m_pos) cannot use 
local 'm_pos' as parameter to non-global template 
SetProperty(Tin, alias Field)(ref Tin param)

I don't understand why that error occurs.

And I cannot find any elegant solutions (even with mixin's) to 
declare a template and then instantiate it in a single line to 
define the methods I want.

Does any of you have an idea?

Thanks

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 12/30/14 8:17 AM, Claude wrote:
 Hello, I'm trying to use templates to define several methods (property
 setters) within a class to avoid some code duplication.
 Here is an attempt:

 class Camera
 {
 private:
      Vector4 m_pos;
      float m_fov, m_ratio, m_near, m_far;
      bool m_matrixCalculated;

 public:
      void SetProperty(Tin, alias Field)(ref Tin param)  property pure  safe
      {
          Field = param;
          m_matrixCalculated = false;
      }

      alias pos   = SetProperty!(float[], m_pos);
      alias pos   = SetProperty!(Vector4, m_pos);
      alias ratio = SetProperty!(float,   m_ratio);
      alias near  = SetProperty!(float,   m_near);
      alias far   = SetProperty!(float,   m_far);
 }

 I get this kind of compilation error:
 Error: template instance SetProperty!(float[], m_pos) cannot use local
 'm_pos' as parameter to non-global template SetProperty(Tin, alias
 Field)(ref Tin param)

 I don't understand why that error occurs.

I think it has to do with the fact that when you are defining the 
aliases, m_pos for example, is an *instance* member so requires an 
instance to get an alias.

What you are probably better off doing is:

void SetProperty(Tin, string Field)(ref Tin param)  property pure  safe
{
    mixin(Field ~ " = param;");
    m_matrixCalculated = false;
}

alias pos = SetProperty!(float[], "m_pos");

I would also put some strict template constraints on the Field string 
too, because one abuse SetProperty pretty easily there.

-Steve

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 12/30/14 8:48 AM, Steven Schveighoffer wrote:

 I think it has to do with the fact that when you are defining the
 aliases, m_pos for example, is an *instance* member so requires an
 instance to get an alias.

 What you are probably better off doing is:

 void SetProperty(Tin, string Field)(ref Tin param)  property pure  safe
 {
     mixin(Field ~ " = param;");
     m_matrixCalculated = false;
 }

 alias pos = SetProperty!(float[], "m_pos");

 I would also put some strict template constraints on the Field string
 too, because one abuse SetProperty pretty easily there.

A possibly more elegant solution, use opDispatch:

void opDispatch(string Field, Tin)(ref Tin param)  property pure  safe 
if(Field == "pos" || Field == "ratio" || ...)
{
    mixin("m_" ~ Field ~ " = param;");
    m_matrixCalculated = false;
}

Not sure if opDispatch works as a  property this way...

-Steve

Daniel =?UTF-8?B?S296w6Fr?= via Digitalmars-d-learn writes:

V Tue, 30 Dec 2014 13:17:08 +0000
Claude via Digitalmars-d-learn <digitalmars-d-learn puremagic.com>
napsáno:

 Hello, I'm trying to use templates to define several methods 
 (property setters) within a class to avoid some code duplication.
 Here is an attempt:
 
 class Camera
 {
 private:
      Vector4 m_pos;
      float m_fov, m_ratio, m_near, m_far;
      bool m_matrixCalculated;
 
 public:
      void SetProperty(Tin, alias Field)(ref Tin param)  property 
 pure  safe
      {
          Field = param;
          m_matrixCalculated = false;
      }
 
      alias pos   = SetProperty!(float[], m_pos);
      alias pos   = SetProperty!(Vector4, m_pos);
      alias ratio = SetProperty!(float,   m_ratio);
      alias near  = SetProperty!(float,   m_near);
      alias far   = SetProperty!(float,   m_far);
 }
 
 I get this kind of compilation error:
 Error: template instance SetProperty!(float[], m_pos) cannot use 
 local 'm_pos' as parameter to non-global template 
 SetProperty(Tin, alias Field)(ref Tin param)
 
 I don't understand why that error occurs.
 
 And I cannot find any elegant solutions (even with mixin's) to 
 declare a template and then instantiate it in a single line to 
 define the methods I want.
 
 Does any of you have an idea?

 
 Thanks

class Camera
{
private:
    int m_pos;
    float m_fov, m_ratio, m_near, m_far;
    bool m_matrixCalculated;
    
public:
    mixin template opAssign(alias Field) {
        void opAssign(Tin)(auto ref Tin param)  property pure  safe
        {
            Field = param;
            m_matrixCalculated = false;
        }
    }

    mixin opAssign!(m_pos)   pos;
    mixin opAssign!(m_fov)   fov;
    mixin opAssign!(m_ratio) ratio;
    mixin opAssign!(m_near)  near;
    mixin opAssign!(m_far)   far;

}

void main() {

    Camera cam = new Camera();

    cam.fov = 1.0;
    stdin.readln;
}

"Claude" <no no.no> writes:

Thanks Steven and Daniel for your explanations.

     mixin template opAssign(alias Field) {
         void opAssign(Tin)(auto ref Tin param)  property pure 
  safe
         {
             Field = param;
             m_matrixCalculated = false;
         }
     }

     mixin opAssign!(m_pos)   pos;

I tested both the "string mixin" and "opAssign" implementations, 
and they work like a charm.
I would have never thought of using both  property and 
"opAssign", but it looks like a secure way of doing it for the 
compilation fails nicely if I type a wrong field in.

src/camera.d(58): Error: undefined identifier m_os, did you mean 
variable m_pos?

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

On 12/30/2014 05:17 AM, Claude wrote:

 use templates to define several methods (property
 setters) within a class to avoid some code duplication.

I just saw this post, which is essentially the same question as Basile 
Burg's. I hope that a college (in France?) is teaching D and that this 
is a homework assignment. Cool stuff! :)

Ali

"Claude" <no no.no> writes:

 I just saw this post, which is essentially the same question as 
 Basile Burg's. I hope that a college (in France?) is teaching D 
 and that this is a homework assignment. Cool stuff! :)

Maybe using templates to create properties is a bit overkill in 
this example. But I could not solve what I thought would be a 
very simple and straightforward "template use-case" (initially 
I'm an embedded RT system C/asm developer).

I'm doing this for a personal project of a 3D engine. As I know 
little about C++/Java or other OO language, I thought I would do 
it directly in D, which seems very promising to me (but 
unfortunately not taught in France as far as I know).