What is the proper way to do a foreach loop with an Array/Map in dart?

May 12, 2022, at 6:10 PM

I'm trying to convert a piece of PHP code to dart and getting stuck. What I have is a PHP array text that gets run through a function called toUTF8 as follows:

if(is_array($text))
{
  foreach($text as $k => $v)
    {
    text[$k] = self::toUTF8($v);
    }
  return $text;
}

Conceptually, what I've done in dart is turn text into a Map

if(text is Map)
{
  foreach(text as k => v)
    {
    text[k] = toUTF8(v);
    }
  return text;
}

But I cannot wrap my mind around, how I would walk the map and run each element into the toUTF8 function.

Essentially, the question is how to do a foreach on a map?

For bonus points, would treating it as a List is a better approach? What this code is ultimately doing is handling malformed UTF8 characters

Answer 1

I'd probably keep it as an array. I don't see any good reason for using a map.

What are the contents of the text array? Is it strings or UTF-8 bytes? Is it individual string characters, or longer strings? Since you call something called toUTF8, I'm assuming it's strings, and you want to convert them to UTF-8. I'm not sure how the code "handles" malformed UTF-8 sequences, since it appears to convert to UTF-8.

You are doing that on a chunk-by-chunk basis, but that's not necessarily correct, if the text array represents a single large text chopped into pieces. Dart strings are sequences of UTF-16 code units, and a surrogate pair can be split between separate chunks, but must be converted together.

I'd do something like:

var bytes = Stream.fromIterable(text).transform(utf8.encoder);
// do something with `bytes`.

or, if you want manual control:

import "dart:convert";
import "dart:typed_data";
// ...
  var buffer = BytesBuilder();
  var converter = utf8.encoder.startChunkedEncoding(
      ByteConversionSink.withCallback(buffer.add));
  text.forEach(converter.add);
  converter.close();
  var bytes = buffer.takeBytes(); // UTF-8 converted `text`.