Text.Join

Summary#

Text.Join(separator, values) concatenates the elements of values into a single string, inserting separator between each adjacent pair. It is the inverse of Text.Split, and identical to string.Join(separator, values).

Signature#

Text.Join(<string> separator, <list> values) -> string
string.Join(<string> separator, <list> values) -> string   // the same operation

Description#

The separator goes only between elements, never at the ends: joining ["a", "b", "c"] with ", " gives "a, b, c" — two separators for three elements. Two consequences follow directly:

• an empty list joins to "" (no elements, so no separators);
• a single-element list joins to just that element (nothing to put a separator between).

An empty separator simply concatenates: Text.Join("", ["a", "b"]) is "ab".

Text.Join and Text.Split are exact inverses when the separator does not itself appear inside an element: splitting on ", " and re-joining on ", " returns the original string. Text.Join runs in memory — it builds one string from a set of values already in hand.

Examples#

// Split a CSV line, drop the empties, and re-join with a cleaner separator.
string Reflow(string csv) {
  return Text.Join(" · ", Text.Split(csv, ","));
}

[Test]
void Text_join_answers() {
  Assert.Equal("a · b · c", Reflow("a,b,c"));

  // Round-trip: split then join on the same separator returns the original.
  Assert.Equal("one, two, three", Text.Join(", ", Text.Split("one, two, three", ", ")));

  // A single element gets no separator; an empty separator just concatenates.
  Assert.Equal("solo", Text.Join(", ", Text.Split("solo", ",")));
  Assert.Equal("ab", Text.Join("", Text.Split("a,b", ",")));
}

See also#

• Text.Split — the inverse: string → list
• String interpolation & format specifiers — $"{a}-{b}", the other way to build a string from values
• Text.Length, Text.IsEmpty, Text.IsBlank, Text.Contains, Text.StartsWith, Text.EndsWith — asking questions about the resulting string