Re: Weird UFC and opCall issues

[Darrell via Digitalmars-d-learn]

Ooops.
Test() wasn't valid.
Still working to create a range object that iterates over an 
internal data struct. But this was may error.



On Saturday, 3 January 2015 at 20:26:41 UTC, Darrell wrote:

Fails with:
t.d(34): Error: need 'this' for 'opCall' of type 'int()'

Also opCall seems to be required to create a range.

class Test
{
  int opCall()
  {
return 1;
  }

  @property int front()
  {
return 2;
  }

  void popFront()
  {
  }

  @property bool empty()
  {
return false;
  }

};

void main(){
  ubyte [] p1;
  Test();
}

Re: Weird UFC and opCall issues

[Darrell via Digitalmars-d-learn]

Seems when creating your own ranges they can't be a class.
Must be a struct or Segmentation fault (core dumped) will follow.

This works as long as Test is a struct.

struct Test
{
  @property int front()
  {
return 2;
  }

  void popFront()
  {
  }

  enum bool empty = false;
};

static assert(isInputRange!Test);

void mainx(){
  Test x;
  writeln(x.take(1));
}

Re: Weird UFC and opCall issues

[Darrell via Digitalmars-d-learn]

Fails with:
t.d(34): Error: need 'this' for 'opCall' of type 'int()'

Also opCall seems to be required to create a range.

class Test
{
  int opCall()
  {
return 1;
  }

  @property int front()
  {
return 2;
  }

  void popFront()
  {
  }

  @property bool empty()
  {
return false;
  }

};

void main(){
  ubyte [] p1;
  Test();
}

Re: Weird UFC and opCall issues

[ted via Digitalmars-d-learn]

Darrell wrote:

 Seems when creating your own ranges they can't be a class.
 Must be a struct or Segmentation fault (core dumped) will follow.
 
 This works as long as Test is a struct.
 
 struct Test
 {
@property int front()
{
  return 2;
}
 
void popFront()
{
}
 
enum bool empty = false;
 };
 
 static assert(isInputRange!Test);
 
 void mainx(){
Test x;
writeln(x.take(1));
 }


With classes, you need to create an instance, so (adjusting some of your 
previous code) this works:

import std.range;
import std.stdio;

class Test
{
   @property int front()
   {
 return 2;
   }

   void popFront()
   {
   }

   @property bool empty()
   {
 return false;
   }

};
static assert(isInputRange!Test);

void main(){
   ubyte [] p1;
Test myTest = new Test();
writeln(myTest.take(1));
}

Re: Weird UFC and opCall issues

[Ali Çehreli via Digitalmars-d-learn]

On 01/03/2015 12:26 PM, Darrell wrote:

 Fails with:
  t.d(34): Error: need 'this' for 'opCall' of type 'int()'

 Also opCall seems to be required to create a range.

D has a feature that does not exists e.g. in C++: You can call the type 
itself as a function. The 'Test()' syntax is a call to that type's 
static opCall().



 class Test
 {
int opCall()
{
  return 1;
}

Not being static, that would require an instance of the Test class.


@property int front()
{
  return 2;
}

You may want to define that member function 'const' as well.


void popFront()
{
}

@property bool empty()
{
  return false;
}

That can be 'const' as well.


 };

D does not require that semicolon.


 void main(){
ubyte [] p1;
Test();
 }

I am removing the opCall and assuming that you actually want a ubyte I 
am returning a ubyte from front().


Also note the almost-mandatory-with-ranges convenience function 'test()' 
below, which hides the invocation of 'new':


class Test
{
  @property ubyte front()
  {
return 2;
  }

  void popFront()
  {
  }

  @property bool empty()
  {
return false;
  }
}

Test test()
{
return new Test();
}

/* Alternatively, you can move test() inside Test as a static opCall:

static Test opCall()
{
return new Test();
}

Then, the syntax in main could be

ubyte [] p1 = Test().take(3).array;

*/

import std.stdio;
import std.range;

void main(){
  ubyte [] p1 = test().take(3).array;
  assert(p1 == [ 2, 2, 2 ]);
}

Ali

Re: Weird UFC and opCall issues

[Darrell via Digitalmars-d-learn]

Thanks for the feedback.


With classes, you need to create an instance


Need to read up classes vs struct.

This bit of syntax was very intresting.

/* Alternatively, you can move test() inside Test as a static 
opCall:


static Test opCall()
{
return new Test();
}

Then, the syntax in main could be

ubyte [] p1 = Test().take(3).array;

*/


Very impressed with D and starting a new job. Might be able to 
use it.

Re: Weird UFC and opCall issues

[Adam D. Ruppe via Digitalmars-d-learn]

On Thursday, 18 December 2014 at 02:42:32 UTC, Jay Pinkman wrote:
source/main.d(12): Error: need 'this' for 'opCall' of type 
'void(string y)'


D doesn't have a really clean separation between static and 
non-static methods. It sees an opCall and thinks you're trying to 
call it, but since it isn't static, it complains you don't have a 
this.



source/main.d(13): Error: no property 'x' for type 'string'


I don't think UFCS works with structs nor local variables anyway, 
so this error makes sense to me.

Re: Weird UFC and opCall issues

[Jay Pinkman via Digitalmars-d-learn]

On Thursday, 18 December 2014 at 02:45:01 UTC, Adam D. Ruppe 
wrote:
D doesn't have a really clean separation between static and 
non-static methods.


hmm.. i thought that's what 'static' is for.

It sees an opCall and thinks you're trying to call it, but 
since it isn't static, it complains you don't have a this.


so it's bug i should report or some idiosyncracy?

I don't think UFCS works with structs nor local variables 
anyway, so this error makes sense to me.


i guess i should request this. in my other code i use a struct to 
represent a transformation so it makes perfect sense to use it in 
UFCS fashion.