Boy, std.bitmanip.bigEndianToNative is annoying to use

[Jonathan M Davis via Digitalmars-d]

On Friday, 22 May 2015 at 19:10:41 UTC, H. S. Teoh wrote:
> In the spirit of forum bickering, ;-) I stumbled upon this D 
> wart today:
> I'm reading some data from a file into a ubyte[] buffer, and I 
> want to
> use bigEndianToNative to convert ushort values in the file data 
> into
> native byte order (whatever the native order might be).
>
> Sounds simple, right? Unfortunately, bigEndianToNative asks for 
> ubyte[n]
> as input. Meaning, this doesn't work:
>
> 	ubyte[] buf = ... /* allocate buffer here */;
> 	file.rawRead(buf);	// Read the data
>
> 	ushort myValue = bigEndianToNative!ushort(buf[4 .. 8]); // NG
>
> The last line doesn't compile, 'cos you can't convert a slice 
> of ubyte[]
> into ubyte[4].
>
> I can think of no easy way to declare a temporary ubyte[4] to 
> make
> bigEndianToNative happy, other than this silly verbosity:
>
> 	ubyte[4] tmp;
> 	tmp[] = buf[4 .. 8];
> 	ushort myValue = bigEndianToNative!ushort(tmp);
>
> and I have to do this for every single numerical field in the 
> data
> buffer that I need to convert. :-(  Why should I copy data 
> around that's
> already sitting in a ubyte[] buffer intended precisely for the 
> purpose
> of doing such conversions in the first place??
>
> The docs for bigEndianToNative claims that this is to help 
> "prevent
> accidentally using a swapped value as a regular one". But I 
> say, "Why,
> oh why???" :-(
>
> This is a very anti-user kind of API. How did we think such a
> straitjacketed API was a good idea in the first place?!

Isn't the problem that you're trying to convert to a ushort, and 
a ushort is _2_ bytes, not 4? If you sliced it correctly, it 
would compile. For instance, this code compiles just fine for me 
with dmd master:

void main()
{
     import std.bitmanip;
     auto buf = new ubyte[](32);
     auto result = bigEndianToNative!ushort(buf[0 .. 2]);
}

But if I change it to buf[0 .. 4], then it fails to compile. So, 
the fact that bigEndianToNative is taking a static array is 
actually catching a bug for you.

- Jonathan M Davis