http://d.puremagic.com/issues/show_bug.cgi?id=7459

           Summary: working around nested function declaration order
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: spec
          Severity: enhancement
          Priority: P2
         Component: websites
        AssignedTo: nobody@puremagic.com
        ReportedBy: timon.gehr@gmx.ch


--- Comment #0 from timon.gehr@gmx.ch 2012-02-07 11:04:28 PST ---
d-programming-language.org/function sez:

Unlike module level declarations, declarations within function scope are processed in order. This means that two nested functions cannot mutually call each other:

void test() {
  void foo() { bar(); } // error, bar not defined
  void bar() { foo(); } // ok
}

The solution is to use a delegate:

void test() {
  void delegate() fp;
  void foo() { fp(); }
  void bar() { foo(); }
  fp = &bar;
}

The proposed solution is unnecessarily complicated and non-optimal. Since nested template functions are instantiated with the state of the symbol table of the lexically first instantiation, this is a superior solution:

void test() {
    void foo()() { bar(); } // ok
    void bar()   { foo(); } // ok
}

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--- Comment #1 from hsteoh@quickfur.ath.cx 2012-12-13 22:29:06 PST ---
Ideally, the compiler should allow nested functions to call each other. I understand there are some complications with how declarations inside function scope are processed, but is there a way to treat function declarations differently from variable declarations?

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--- Comment #2 from timon.gehr@gmx.ch 2012-12-14 00:20:08 PST ---
(In reply to comment #1)
> Ideally, the compiler should allow nested functions to call each other.

I agree. Furthermore, ideally the state of the symbol table should the one at the declaration of the template.

> I understand there are some complications with how declarations inside function scope are processed, but is there a way to treat function declarations differently from variable declarations?

There are no complications specific to local declarations, except maybe some kind of conservative definite initalization analysis. I guess it's just not implemented and the spec has been modelled after the implementation. An implementation would have to make sure to handle mixins correctly. (just looking at syntactic properties is not enough to decide whether something can be forward-referenced because of those.)

string foo(){ return "foo"; }

void fun(){
    string gen(){ return "void "~foo()~"(){ return `baz`; } ";
    mixin(gen());
}

The above code should be a compiler error. (Similar examples can be constructed
in unordered scopes.)

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--- Comment #3 from timon.gehr@gmx.ch 2012-12-14 00:21:05 PST ---
(In reply to comment #2)
> ...
> 
> The above code should be a compiler error.

/compiler/compile/s

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Andrej Mitrovic <andrej.mitrovich@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich@gmail.com


--- Comment #4 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-02-06 20:38:11 PST ---
Another workaround:

mixin template A()
{
    void foo() { bar(); } // ok
    void bar() { foo(); } // ok
}

void main()
{
    void test() { }
    mixin A!();
}

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