• Tim K. (40/40) Jun 06 2015 Hello!
• Manfred Nowak (5/6) Jun 06 2015 x is not initialized.
• Tim K. (7/10) Jun 06 2015 Thank you two.
• "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> (8/17) Jun 06 2015 Because `SList` is a struct, which is a value type that is
• Tim K. (5/12) Jun 06 2015 That makes sense. I overlooked that in SList's documentation and
• Panke (3/14) Jun 06 2015 Best way to construct a std.container is to use
• Jonathan M Davis via Digitalmars-d-learn (12/51) Jun 06 2015 has nothing to do with SList. It's the fact that you're trying to

"Tim K." <invalid webinterface.com> writes:

Hello!


background.
Hello World was working, so I figured that I should try something 
more complex: a template class and si I went with a simple stack.

Using dmd the code I wrote causes a segmentation fault and I am 
not sure why.

import std.stdio;
import std.container.slist;


class Stack(T)
{
     SList!(T) s;
     this() {}
     void push(T element)
     {
         s.insertFront(element);
     }
}

int main()
{
     Stack!(int) x;
     writeln("1");
     SList!(int) p;
     writeln("2");
     p.insertFront(42);
     writeln("3");
     x.push(42);
     writeln("4");
     return 0;
}


This program prints the following into the console:
% dmd test.d && ./test
1
2
3
zsh: segmentation fault  ./test


I do not understand why the normal SList works fine but the one 
inside the object doesn't. What am I overlooking?


Best regards,
Tim

Manfred Nowak <svv1999 hotmail.com> writes:

Tim K. wrote:

      Stack!(int) x;

x is not initialized.

`auto x= new Stack!(int);'
will do.

-manfred

"Tim K." <invalid webinterface.com> writes:

On Saturday, 6 June 2015 at 10:10:15 UTC, Manfred Nowak wrote:
 x is not initialized.

 `auto x= new Stack!(int);'
 will do.

Thank you two.
But that leads me to another question: Why do I need to 
initialize x with a "new Stack" but I don't need to initialize p 
with a "new SList"?

Best regards,
Tim

"Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:

On Saturday, 6 June 2015 at 10:16:12 UTC, Tim K. wrote:
 On Saturday, 6 June 2015 at 10:10:15 UTC, Manfred Nowak wrote:
 x is not initialized.

 `auto x= new Stack!(int);'
 will do.

 Thank you two.
 But that leads me to another question: Why do I need to 
 initialize x with a "new Stack" but I don't need to initialize 
 p with a "new SList"?

Because `SList` is a struct, which is a value type that is 
allocated where you declare it (here on the stack), while you 
used a class, which is a reference type and has to be allocated 
with `new`.

You can also turn your `Stack` type into a struct, then it works, 
too. (You just need to remove the constructor, which is empty 
anyway.)

"Tim K." <invalid webinterface.com> writes:

On Saturday, 6 June 2015 at 10:20:34 UTC, Marc Schütz wrote:

 Because `SList` is a struct, which is a value type that is 
 allocated where you declare it (here on the stack), while you 
 used a class, which is a reference type and has to be allocated 
 with `new`.

 You can also turn your `Stack` type into a struct, then it 
 works, too. (You just need to remove the constructor, which is 
 empty anyway.)

That makes sense. I overlooked that in SList's documentation and 
thought it was just a regular old class, too.

Best regards,
Tim

"Panke" <tobias pankrath.net> writes:

On Saturday, 6 June 2015 at 10:16:12 UTC, Tim K. wrote:
 On Saturday, 6 June 2015 at 10:10:15 UTC, Manfred Nowak wrote:
 x is not initialized.

 `auto x= new Stack!(int);'
 will do.

 Thank you two.
 But that leads me to another question: Why do I need to 
 initialize x with a "new Stack" but I don't need to initialize 
 p with a "new SList"?

 Best regards,
 Tim

Best way to construct a std.container is to use 
std.container.make.

Jonathan M Davis via Digitalmars-d-learn writes:

On Saturday, June 06, 2015 09:44:36 Tim K. via Digitalmars-d-learn wrote:
 Hello!


 background.
 Hello World was working, so I figured that I should try something
 more complex: a template class and si I went with a simple stack.

 Using dmd the code I wrote causes a segmentation fault and I am
 not sure why.

 import std.stdio;
 import std.container.slist;


 class Stack(T)
 {
      SList!(T) s;
      this() {}
      void push(T element)
      {
          s.insertFront(element);
      }
 }

 int main()
 {
      Stack!(int) x;
      writeln("1");
      SList!(int) p;
      writeln("2");
      p.insertFront(42);
      writeln("3");
      x.push(42);
      writeln("4");
      return 0;
 }


 This program prints the following into the console:
 % dmd test.d && ./test
 1
 2
 3
 zsh: segmentation fault  ./test


 I do not understand why the normal SList works fine but the one
 inside the object doesn't. What am I overlooking?

From the looks of it, you never initialized x, so it's null. So, the problem

has nothing to do with SList. It's the fact that you're trying to
dereference a null reference. You need to call new to allocate a Stack!int,
not just declare a reference to one.

void main()
{
    Stack!int x
    x.push(42);
}

would have exactly the same problem. You need something like

auto x = new Stack!int;

- Jonathan M Davis