interpolate function

String interpolate(Locale locale, String string, Map<String, dynamic> variables, I18NextOptions options,)

Replaces occurrences of matches in string for the named values in options (if they exist), by first passing through the I18NextOptions.formats before joining the resulting string.

• 'Hello {{name}}' + {name: 'World'} -> 'Hello World'. This example illustrates a simple interpolation.
• 'Now is {{date, dd/MM}}' + {date: DateTime.now()} -> 'Now is 23/09'. In this example, I18NextOptions.formats must be able to properly format the date.
• 'A string with {{grouped.key}}' + {'grouped': {'key': "grouped keys}} -> 'A string with grouped keys'. In this example the variables are in the grouped formation (denoted by the I18NextOptions.keySeparator).

Implementation

String interpolate(
  Locale locale,
  String string,
  Map<String, dynamic> variables,
  I18NextOptions options,
) {
  final formatSeparator = options.formatSeparator ?? ',';
  final keySeparator = options.keySeparator ?? '.';
  final escapeValue = options.escapeValue ?? true;

  final todo = [
    _InterpolationHelper(
      interpolationUnescapePattern(options),
      (input) => input,
    ),
    _InterpolationHelper(
      interpolationPattern(options),
      escapeValue ? (options.escape ?? escape) : (input) => input,
    ),
  ];

  return todo.fold<String>(
    string,
    (result, helper) => result.splitMapJoin(
      helper.pattern,
      onMatch: (match) {
        var variable = match[1]!.trim();

        Iterable<String> formats = [];
        if (variable.contains(formatSeparator)) {
          final variableParts = variable.split(formatSeparator);
          variable = variableParts.first.trim();
          formats = variableParts.skip(1).map((e) => e.trim());
        }

        if (variable.isEmpty) {
          throw InterpolationException('Missing variable', match);
        }

        final path = variable.split(keySeparator);
        final value = evaluate(path, variables);
        final formatted =
            formatter.format(value, formats, locale, options) ??
            (throw InterpolationException(
              'Could not evaluate or format variable',
              match,
            ));
        return helper.escape(formatted);
      },
    ),
  );
}