• Andre (28/28) Dec 04 2015 Hi,
• Jonathan M Davis via Digitalmars-d-learn (18/42) Dec 04 2015 You cannot use symbols before you declare them in a function (even if
• Artur Skawina via Digitalmars-d-learn (38/69) Dec 04 2015 No, it's how D is designed -- inside functions the order of
• Andre (4/39) Dec 04 2015 Thanks for the clarifications and the example.

Andre <andre s-e-a-p.de> writes:

Hi,

I have a strange issue with following coding.

void baz(); // forward declaration

void foo()
{
	void bar()
	{
		baz(); // (1) without f.d. syntax error
	}
	
	void baz()
	{
		bar();
	}
	
	baz(); // (2) No linker error if line is removed
}

void main()
{
	foo();
}

Without the forward declaration, there is a syntax error at (1)
With the forward declaration there is no syntax error but
a linker error at (2). This linker error disappears if line at (2)
is removed.
It looks like a bug, is it?

Kin regards
Andre

Jonathan M Davis via Digitalmars-d-learn writes:

On Friday, December 04, 2015 08:12:05 Andre via Digitalmars-d-learn wrote:
 Hi,

 I have a strange issue with following coding.

 void baz(); // forward declaration

 void foo()
 {
   void bar()
   {
       baz(); // (1) without f.d. syntax error
   }

   void baz()
   {
       bar();
   }

   baz(); // (2) No linker error if line is removed
 }

 void main()
 {
   foo();
 }

 Without the forward declaration, there is a syntax error at (1)
 With the forward declaration there is no syntax error but
 a linker error at (2). This linker error disappears if line at (2)
 is removed.
 It looks like a bug, is it?

You cannot use symbols before you declare them in a function (even if
they're nested functions), and you can't forward declare them. When you
declare baz outside of foo, bar is now trying to use a different baz from
the one that you declare after it. Rather, it's trying to use one that's at
the module-level, not a nested function. And you never defined that baz. So,
you get a linker error when you use it. What's going on would be clearer if
you used distinct names:


void module_baz();

void foo()
{
    void bar() { module_baz(); }
    void baz() { bar(); }

    baz();
}


While that may not be what you're trying to do, it's what you're actually
doing. Mutually recursive nested functions aren't possible in D.

- Jonathan M Davis

Artur Skawina via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:

On 12/04/15 09:12, Andre via Digitalmars-d-learn wrote:
 Hi,
 
 I have a strange issue with following coding.
 
 void baz(); // forward declaration
 
 void foo()
 {
     void bar()
     {
         baz(); // (1) without f.d. syntax error
     }
     
     void baz()
     {
         bar();
     }
     
     baz(); // (2) No linker error if line is removed
 }
 
 void main()
 {
     foo();
 }
 
 Without the forward declaration, there is a syntax error at (1)
 With the forward declaration there is no syntax error but
 a linker error at (2). This linker error disappears if line at (2)
 is removed.
 It looks like a bug, is it?

No, it's how D is designed -- inside functions the order of
declarations matters (and forward declarations don't work).

Your version wrongly declares another `baz` at module scope,
and, as there's no definition, you end up with the linker error.

Two workarounds:

1) Templatize the functions:

   void foo()
   {
      void bar()()
      {
          baz();
      }
    
      void baz()()
      {
          bar();
      }
    
      baz();
   }

2) Use a struct:

   void foo()
   {
      struct Hack {
         void bar()
         {
             baz();
         }

         void baz()
         {
             bar();
         }
      }

      Hack hack;

      hack.baz();
   }

artur

Andre <andre s-e-a-p.de> writes:

On Friday, 4 December 2015 at 09:51:30 UTC, Artur Skawina wrote:

 No, it's how D is designed -- inside functions the order of 
 declarations matters (and forward declarations don't work).

 Your version wrongly declares another `baz` at module scope, 
 and, as there's no definition, you end up with the linker error.

 Two workarounds:

 1) Templatize the functions:

    void foo()
    {
       void bar()()
       {
           baz();
       }

       void baz()()
       {
           bar();
       }

       baz();
    }

 2) Use a struct:

    void foo()
    {
       struct Hack {
          void bar()
          {
              baz();
          }

          void baz()
          {
              bar();
          }
       }

       Hack hack;

       hack.baz();
    }

 artur

Thanks for the clarifications and the example.

Kind regards
André