Function Encoder.writeMapStart

Call this to start a new map. See [writeArrayStart] for details on usage.

abstract void writeMapStart() @safe;

As an example of usage, let's say you want to write a map of records, the record consisting of an Long field and a Boolean field. Your code would look something like this: 

out.writeMapStart();
out.setItemCount(list.size());
foreach (string key, GenericRecord value; map) {
  out.startItem();
  out.writeString(key);
  out.writeLong(value.getField("longField").getValue!long);
  out.writeBoolean(value.getField("boolField").getValue!bool);
}
out.writeMapEnd();

Throws

AvroTypeException If this is a stateful writer and a map is not expected