*[<Null safety>](https://dart.dev/null-safety)*
PseudoFile.readWrite(int _capacity, ReadFn? _readFn, WriteFn? _writeFn)
PseudoFile.readWrite(this._capacity, this._readFn, this._writeFn) : assert(_writeFn != null), assert(_readFn != null), assert(_capacity > 0);