join method
Converts each element to a String and concatenates the strings.
Iterates through elements of this iterable,
converts each one to a String by calling Object.toString,
and then concatenates the strings, with the
separator
string interleaved between the elements.
Example:
final planetsByMass = <double, String>{0.06: 'Mercury', 0.81: 'Venus',
0.11: 'Mars'};
final joinedNames = planetsByMass.values.join('-'); // Mercury-Venus-Mars
Implementation
@override
String join([String separator = '']) => throw UnsupportedError('join');