https://d.puremagic.com/issues/show_bug.cgi?id=12359

           Summary: implicit overload merging with selective/renamed
                    imports should be removed
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: k.hara.pg@gmail.com


--- Comment #0 from Kenji Hara <k.hara.pg@gmail.com> 2014-03-13 17:22:11 PDT ---
Currently, selective or renamed imports create alias declaration implicitly.

  import a : b;
  // is mostly equivalent with:
  // import a; alias b = a.b;

  import a : x = b;
  // is mostly equivalent with:
  // import a; alias x = a.b;

But it is problematic behavior, because it would implicitly merge overloads in the imported module. For example:

  import std.ascii : isDigit;   // bool isDigit(dchar c)

  bool isDigit(char c) { return true; }
  // Here isDigit is an overload set of bool(char) and bool(dchar)

  void main() {
    dchar d = 'a';
    isDigit(d);   // matches to std.ascii.isDiigt
  }

I think import declarations should only handle symbol visibility. So the current behavior is not orthogonal. Therefore it should be deprecated and finally removed.

To reproduce same behavior, explicit alias should work.

  import std.ascii : isDigit;   // Don't create alias silently

  bool isDigit(char c) { return true; }
  alias isDigit = std.ascii.isDigit;  // explicitly merge overloads

  void main() {
    dchar d = 'a';
    isDigit(d);   // matches to std.ascii.isDiigt
  }

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Kenji Hara <k.hara.pg@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull


--- Comment #1 from Kenji Hara <k.hara.pg@gmail.com> 2014-03-13 17:59:49 PDT ---
The compiler change to show deprecation messages:

https://github.com/D-Programming-Language/dmd/pull/2256

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

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


--- Comment #2 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2014-03-14 00:22:31 PDT ---
(In reply to comment #0)
> To reproduce same behavior, explicit alias should work.
> 
>   import std.ascii : isDigit;   // Don't create alias silently
> 
>   bool isDigit(char c) { return true; }
>   alias isDigit = std.ascii.isDigit;  // explicitly merge overloads

I don't see how this can work, "std.ascii" should not be visible in the last statement.

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--- Comment #3 from Kenji Hara <k.hara.pg@gmail.com> 2014-03-14 06:55:24 PDT ---
(In reply to comment #2)
> (In reply to comment #0)
> > To reproduce same behavior, explicit alias should work.
> > 
> >   import std.ascii : isDigit;   // Don't create alias silently
> > 
> >   bool isDigit(char c) { return true; }
> >   alias isDigit = std.ascii.isDigit;  // explicitly merge overloads
> 
> I don't see how this can work, "std.ascii" should not be visible in the last statement.

I think selective imports should make the fully qualified module name still visible. It's consistent behavior with basic imports.

====

For the future enhancement, I'm planning to add variations of import declarations. Just the ideas:

1. static selective import

  static import std.stdio : writeln;
  //writeln();  // NG
  std.stdio.writeln();  // OK
  //std.stdio.writefln("");  // NG

2. static renamed import

  static import io = std.stdio;
  //writeln();  // NG
  //std.stdio.writeln();  // NG
  io.writeln();  // OK

3. static selective renamed import

  static import io = std.stdio : writeln;
  io.writeln();  // OK
  //io.writefln("");  // NG

4. unnamed import

  import = std.stdio;
  writeln();  // OK
  writefln("");  // OK
  //std.stdio.writeln();  // NG

5. unnamed selective import

  import = std.stdio : writeln;
  writeln();  // OK
  //writefln("");  // NG
  //std.stdio.writeln();  // NG

They are much flexible than the current behavior. Increasing orthogonality will give to programmers the ability to control imported names more precisely.

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--- Comment #4 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2014-03-14 07:14:39 PDT ---
(In reply to comment #3)
> I think selective imports should make the fully qualified module name still visible. It's consistent behavior with basic imports.

Ok.

> 4. unnamed import
> 
>   import = std.stdio;
>   writeln();  // OK
>   writefln("");  // OK
>   //std.stdio.writeln();  // NG

My initial reaction is that I'm not a fan of this syntax. But anyway, we can discuss this later.

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs@eml.cc


--- Comment #5 from bearophile_hugs@eml.cc 2014-03-14 07:18:01 PDT ---
(In reply to comment #3)

> 4. unnamed import
> 
>   import = std.stdio;
>   writeln();  // OK
>   writefln("");  // OK
>   //std.stdio.writeln();  // NG
> 
> 5. unnamed selective import
> 
>   import = std.stdio : writeln;
>   writeln();  // OK
>   //writefln("");  // NG
>   //std.stdio.writeln();  // NG

This will need to be discussed. I don't like this a lot. What's the purpose of this?

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--- Comment #6 from Kenji Hara <k.hara.pg@gmail.com> 2014-03-14 07:36:42 PDT ---
(In reply to comment #5)
> (In reply to comment #3)
> 
> > 4. unnamed import
> > 
> >   import = std.stdio;
> >   writeln();  // OK
> >   writefln("");  // OK
> >   //std.stdio.writeln();  // NG
> > 
> > 5. unnamed selective import
> > 
> >   import = std.stdio : writeln;
> >   writeln();  // OK
> >   //writefln("");  // NG
> >   //std.stdio.writeln();  // NG
> 
> This will need to be discussed. I don't like this a lot. What's the purpose of this?

They are just funny ideas to mask fully qualified names.

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--- Comment #7 from github-bugzilla@puremagic.com 2014-03-15 16:49:21 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/614158f3e8ca5af8a512120baa24e655bdb57890 Add test case for issue 12359 before deprecation

https://github.com/D-Programming-Language/dmd/commit/45d55309d594446cb509ae1b8d4ba1fa69205bfa
fix Issue 12359 - implicit overload merging with selective/renamed imports
should be removed

Show deprecation message for the implicitly merged overload set, by using cross-module overload set mechanism.

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--- Comment #8 from Kenji Hara <k.hara.pg@gmail.com> 2014-04-02 20:22:40 PDT ---
New pull request: https://github.com/D-Programming-Language/dmd/pull/3416

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Kenji Hara <k.hara.pg@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|implicit overload merging   |implicit overload merging
                   |with selective/renamed      |with selective imports
                   |imports should be removed   |should be removed


--- Comment #9 from Kenji Hara <k.hara.pg@gmail.com> 2014-04-06 21:22:13 PDT ---
Very sorry, I was misused the word "renamed imports" for the feature "selective imports with renaming selected symbols".

I tweak the issue summary.

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