Newbie problem

[Adam D. Ruppe]

On Wednesday, 19 June 2013 at 15:25:15 UTC, Roger Stokes wrote:
> page406x.d(11): Error: cannot implicitly convert expression 
> (__r24.front()) of type ubyte[] to immutable(ubyte)[]

>    foreach (immutable(ubyte)[] buffer; 
> stdin.byChunk(bufferSize)) {


The problem here is that byChunk returns a mutable buffer, type 
ubyte[]. If you said "foreach(ubyte[] buffer; 
stdin.byChunk(bufferSize)) {...}" you should be able to compile 
it.

I think this was changed after the book was written because 
byChunk now reuses its buffer. Each time through the loop, it 
overwrites the old data with the next batch, which means the old 
data cannot be immutable. (The reason for reusing it is to avoid 
allocating new memory for a fresh buffer every time.)

Since you aren't keeping a copy of the buffer, just changing the 
type should be enough for your program to work.

If you needed an immutable copy, if you were going to store it or 
something, the way you'd do that is to call buffer.idup:

foreach(ubyte[] temporaryBuffer; stdin.byChunk(bufferSize) {
      immutable(ubyte)[] permanentBuffer = temporaryBuffer.idup;
     // you can now use the permanentBuffer
}