attribute length missing in std.array: Appender

[via Digitalmars-d-learn]

On Thursday, 27 November 2014 at 16:08:13 UTC, Andre wrote:
> Hi,
>
> I implement a network protocol and use an Appender!(ubyte[])().
> I have following issue. The first three bytes I have to fill,
> the following bytes are reserved and must be 0. In this example
> the overall header length must be 8.
>
> import std.array: appender;
> const HEADER_LENGTH = 8;
> 	
> auto app = appender!(ubyte[])();
> app.put(cast(ubyte)40);
> app.put(cast(ubyte)5);
> app.put(cast(ubyte)234);
> // ... add 5 times 0
> // variable length body will follow
>
> In case of dynamic array I can simple set the length to 8.
> Appender doesn't have a length attribute.
>
> Is there some other nice D functionaliy I can use?
> Maybe some functionality in std.array is missing: app.fill(0, 
> HEADER_LENGTH)?
> Currently I do a work around with a for loop.
>
> Kind regards
> André

You can initialize the appender with an existing array, or put an 
entire array into it at once:

     import std.array: appender;
     ubyte[] temp;
     temp.reserve(8);  // reserve first, so that only one 
allocation happens
     temp[0 .. 3] = [40, 5, 234];
     temp.length = 8;
     auto app = appender!(ubyte[])(temp);
     // or:
     app.put(temp);

The array will not be copied when the appender is constructed.