DART

dart list join

[1,2,3].join(); // "123"
[1,2,3].join(','); // "1,2,3"

dart 2d list join

var a = [[1,2,3], [4,5,6], [7,8,9]];
a.map((e) => e.join(' ')).join('
');
//"1 2 3
// 4 5 6
// 7 8 9"