memoryMap

auto tf = testFile();

immutable newData = "The quick brown fox jumps over the lazy dog.";

// Modify the file
{
    auto f = File(tf.name, FileFlags.readWriteEmpty);
    f.length = newData.length;

    auto map = f.memoryMap!char(Access.readWrite);
    assert(map.length == newData.length);

    map[] = newData[];

    assert(map[0 .. newData.length] == newData[]);
}

// Read the file back in
{
    auto f = File(tf.name, FileFlags.readExisting);
    auto map = f.memoryMap!char(Access.read);
    assert(map.length == newData.length);
    assert(map[0 .. newData.length] == newData[]);
}