Re: inout, delegates, and visitor functions.

[Sebastien Alaiwan via Digitalmars-d-learn]

Hi ponce,
Thanks for your suggestion.
I think I may have found the beginning of a solution:

class E
{
  import std.traits;

  void apply(this F, U)(void delegate(U e) f)
if(is(Unqual!U == E))
  {
f(this);
  }

  int val;
}

int main()
{
  void setToZero(E e)
  {
e.val = 0;
  }

  void printValue(const E e)
  {
import std.stdio;
writefln("Value: %s", e.val);
  }

  E obj;

  obj.apply();
  obj.apply();

  const(E) objConst;
  //objConst.apply();
  objConst.apply();

  return 0;
}


Basically, I avoid the 'const'/'inout' attribute of the 'apply' 
function by using a 'this F' template argument.
Then, I need a second template argument 'U', otherwise, I can't 
call 'printValue' on a non-const E instance.

Re: inout, delegates, and visitor functions.

[ponce via Digitalmars-d-learn]

On Saturday, 24 October 2015 at 11:28:17 UTC, Sebastien Alaiwan 
wrote:

Hi ponce,
Thanks for your suggestion.
I think I may have found the beginning of a solution:

class E
{
  import std.traits;

  void apply(this F, U)(void delegate(U e) f)
if(is(Unqual!U == E))
  {
f(this);
  }

  int val;
}

int main()
{
  void setToZero(E e)
  {
e.val = 0;
  }

  void printValue(const E e)
  {
import std.stdio;
writefln("Value: %s", e.val);
  }

  E obj;

  obj.apply();
  obj.apply();

  const(E) objConst;
  //objConst.apply();
  objConst.apply();

  return 0;
}




Clever. It works because of const inference on template functions.
Didn't know you could use 'this' as a type.

inout, delegates, and visitor functions.

[Sebastien Alaiwan via Digitalmars-d-learn]

Hi all,

I'm trying to get the following code to work.
(This code is a simplified version of some algebraic type).
Is it possible to only declare one version of the 'apply' 
function?

Or should I declare the const version and the non-const version?

I tried using "inout", but I got the following error:

test.d(28): Error: inout method test.E.apply is not callable 
using a mutable object



class E
{
  void apply(void delegate(inout(E) e) f) inout
  {
f(this);
  }

  int val;
}

void m()
{
  void setToZero(E e)
  {
e.val = 0;
  }

  void printValue(const E e)
  {
import std.stdio;
writefln("Value: %s", e.val);
  }

  E obj;

  obj.apply();
  obj.apply();
}

Thanks!

Re: inout, delegates, and visitor functions.

[ponce via Digitalmars-d-learn]

On Saturday, 24 October 2015 at 08:51:58 UTC, Sebastien Alaiwan 
wrote:

Hi all,

I'm trying to get the following code to work.
(This code is a simplified version of some algebraic type).
Is it possible to only declare one version of the 'apply' 
function?

Or should I declare the const version and the non-const version?

I tried using "inout", but I got the following error:

test.d(28): Error: inout method test.E.apply is not callable 
using a mutable object



class E
{
  void apply(void delegate(inout(E) e) f) inout
  {
f(this);
  }

  int val;
}

void m()
{
  void setToZero(E e)
  {
e.val = 0;
  }

  void printValue(const E e)
  {
import std.stdio;
writefln("Value: %s", e.val);
  }

  E obj;

  obj.apply();
  obj.apply();
}

Thanks!




Hi Sebastien,

That was an interesting question and I didn't succeed with 
'inout' either without duplicating apply.
I have a partial solution here: 
http://dpaste.dzfl.pl/b5ec7f16b912 which templatizes the delegate 
type, but is probably not what you want.


The qualifier is not carried on to the apply() function. When 
taking a const delegate it will still not be const.