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

[d-bugmail at puremagic.com]

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 at puremagic.com
        ReportedBy: andrej.mitrovich at gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich at 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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