what is the difference between template and mixin template

[Ali Çehreli]

On 06/10/2012 10:08 AM, Zhenya wrote:
 > Hi!Today I completly understood,what I don't now what is the difference
 > between template and mixin template

There is a terminology problem: there is no such thing as "mixin 
templates". There are only templates.

D also has the mixin feature with two flavors:

- Mixing in template instantiations as code (this is called "template 
mixins")

- Mixing in strings as code (this is called "string mixins")

 >,becouse I think that this should'nt
 > work.But compiler is disagree.Could anybody explain me please?
 >
 > import std.stdio;
 >
 > int x;
 > template smth()
 > {
 > void smth(){x = 1;}
 > }

That is not a very good example because it happens to be an eponymous 
template.

 > void main()
 > {
 > int x;
 > mixin smth;//why it compiles? smth is a regular template

You are instantiating smth, effectively inserting a smth() function 
definition right at this point in code.

 > smth();
 > writeln(.x);
 > writeln(x);
 > readln();
 > }

Here is another example from a yet-untranslated chapter of mine:

template PointArrayFeature(T, size_t count)
{
     import std.stdio;

     T[count] points;

     void setPoint(size_t index, T point)
     {
         points[index] = point;
     }

     void printPoints()
     {
         writeln("All of the points:");

         foreach (i, point; points) {
             write(i, ":", point, ' ');
         }

         writeln();
     }
}

That template defines a feature that combines three pieces of code:

1) An array of points of any type

2) The function setPoint() as a setter

3) The function printPoints()

Such a feature can be mixed in at any point in the program. For example, 
the Line struct needs two points of type int:

struct Line
{
      mixin PointArrayFeature!(int, 2);
}

The Line struct can in turn be used in the program with all the features 
that it has gained by mixing in the PointArrayFeature template:

void main()
{
     auto line = Line();
     line.setPoint(0, 100);
     line.setPoint(1, 200);
     line.printPoints();
}

Ali

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D Programming Language Tutorial: http://ddili.org/ders/d.en/index.html