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digitalmars.D.bugs - [Issue 12489] New: std.bitmanip byte swapping routines should be partially instantiable

reply d-bugmail puremagic.com writes:
https://d.puremagic.com/issues/show_bug.cgi?id=12489

           Summary: std.bitmanip byte swapping routines should be
                    partially instantiable
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: andrej.mitrovich gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2014-03-29
12:15:14 CET ---
I've had a use case for generic endianness swapping when reading file headers,
and was going to use attributes. For example:

struct Header
{
     Converter!(littleEndianToNative!ushort)
    ushort reserved1;
}

Unfortunately this doesn't work because you can't partially instantiate
littleEndianToNative:

Error: template instance littleEndianToNative!ushort does not match template
declaration littleEndianToNative(T, uint n)(ubyte[n] val) if
(canSwapEndianness!T && n == T.sizeof)

It would have to be converted to a template, e.g.:

Before:

-----
T littleEndianToNative(T, size_t n)(ubyte[n] val)  safe pure nothrow
-----

After:

-----
template littleEndianToNative(T)
{
    T littleEndianToNative(size_t n)(ubyte[n] val)  safe pure nothrow
    {
        ...
    }
}
-----

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--- Comment #1 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2014-03-29
12:32:30 CET ---
Here's a somewhat generic wrapper workaround:

-----
template PartialTempl(alias templ, T...)
{
    auto PartialTempl(Args...)(auto ref Args args)
    {
        return templ!T(args);
    }
}
-----

Usable as:


-----
 Converter!(PartialTempl!(littleEndianToNative, ushort))
ushort reserved1;
-----

Of course 'littleEndianToNative' and friends take a ubyte[N], not a ushort, so
in my file loading routine I have to take that into account. But using
attributes is pretty nice.

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

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


--- Comment #2 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2014-03-29
21:01:05 CET ---
(In reply to comment #1)
 Here's a somewhat generic wrapper workaround:
 
 -----
 template PartialTempl(alias templ, T...)
 {
     auto PartialTempl(Args...)(auto ref Args args)
     {
         return templ!T(args);
     }
 }
 -----

This solves it for me. -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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Vladimir Panteleev <thecybershadow gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |thecybershadow gmail.com


--- Comment #3 from Vladimir Panteleev <thecybershadow gmail.com> 2014-03-30
14:37:22 EEST ---
(In reply to comment #0)
      Converter!(littleEndianToNative!ushort)
     ushort reserved1;

I don't know the context, but there's some redundancy here already (ushort is listed twice). Any reason you can't use ` Converter!littleEndianToNative` ? -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #4 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2014-03-30
14:45:56 CEST ---
(In reply to comment #3)
 (In reply to comment #0)
      Converter!(littleEndianToNative!ushort)
     ushort reserved1;

I don't know the context, but there's some redundancy here already (ushort is listed twice). Any reason you can't use ` Converter!littleEndianToNative` ?

Yeah you're right, I don't need to embed this information. It's really nice that I can now write: struct Header { Converter!littleEndianToNative { ushort reserved1; ushort ordnum; ushort insnum; ushort patnum; ushort flags; ushort cwtv; ushort version_; } } -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 30 2014