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digitalmars.D.bugs - [Issue 8983] New: Overload introduced behind mixin template can't be called from another overload

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8983

           Summary: Overload introduced behind mixin template can't be
                    called from another overload
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: turkeyman gmail.com



http://dpaste.dzfl.pl/f955d02a

test(int) can't call the overload text(int, float) introduced behind the mixin
template.
If you paste that mixin directly (remove the mixin template) it works.

Again here:

mixin template MixOverload()
{
    mixin( "int test(int x, float y) { return x + cast(int)y; }" );
}

struct Test
{
    mixin MixOverload; // <- introduce an overload for test()


    void test(int x)
    {
        test(x, 1);    // call the overload defined in the mixin
    }
}

Output:

/home/c950/c254.d(13): Error: function c254.Test.test (int x) is not callable
using argument types (int,int)
/home/c950/c254.d(13): Error: function c254.Test.test (int x) is not callable
using argument types (int,int)
/home/c950/c254.d(13): Error: expected 1 arguments, not 2 for non-variadic
function type void(int x)

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8983


Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com



14:54:35 PST ---
This actually isn't a bug. Inserting a template mixin creates a new nested
scope, and names not in that nested scope override the ones in it.

Your code can be made to work in two ways. But first we need to give a name to
the nested scope:

    mixin MixOverload;

becomes:

    mixin MixOverload nn;

Now, the mixin template names can be prefixed with nn:

    void test(int x)
    {
        nn.test(x, 1);    // call the overload defined in the mixin
    }

which works. Alternatively, the nested scope can be aliased into the current
scope with:

    alias nn.test test;

and now:

    void test(int x)
    {
        test(x, 1);    // call the overload defined in the mixin
    }

will work, as aa.test will be overloaded with test.

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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


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Max Samukha <samukha voliacable.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |samukha voliacable.com



PST ---
One unfortunate consequence of the nested scope rule is we cannot use unnamed
mixins for adding definitions to declarations.

mixin template Foo()
{
   void foo() {}
}

class A
{
   void foo();
   mixin Foo;
}

results in undefined reference.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Maxim Fomin <maxim maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxim maxim-fomin.ru



---


 One unfortunate consequence of the nested scope rule is we cannot use unnamed
 mixins for adding definitions to declarations.
 
 mixin template Foo()
 {
    void foo() {}
 }
 
 class A
 {
    void foo();
    mixin Foo;
 }
 
 results in undefined reference.


Even if there were no nested scope, this still would not work because function
with omitted body is expected to appear in another object file:

class A
{
   void foo();
   void foo() {}
}

void main()
{
    (new A).foo;
}

will fail because foo matches "both foo and foo". This contradicts to C
practice and does not make sense because dmd artificially creates ambiguity
between function declaration and its own body. I complained in Bugzilla but was
told that such practice in redundant in C and need not supported even as
enhancement.

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PST ---



 
 Even if there were no nested scope, this still would not work because function
 with omitted body is expected to appear in another object file:
 


That changed recently. Now 

class A
{
    void foo();
    void foo() {  }

    void bar();
    mixin(q{ void bar() {} });
}

void main()
{
    auto a = new A;
    a.foo();
    a.bar();
}

works as expected.

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---



 

 
 Even if there were no nested scope, this still would not work because function
 with omitted body is expected to appear in another object file:
 


 
 That changed recently. Now 
 
 class A
 {
     void foo();
     void foo() {  }
 
     void bar();
     mixin(q{ void bar() {} });
 }
 
 void main()
 {
     auto a = new A;
     a.foo();
     a.bar();
 }
 
 works as expected.


Do you compile it with version from git? Dmd 2.060 rejects this. When it was
fixed?

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PST ---

git

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PST ---
Note that variable definitions still fail:

extern int x;
int x; // conflict

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