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Function std.algorithm.iteration.joiner

Lazily joins a range of ranges with a separator. The separator itself is a range. If a separator is not provided, then the ranges are joined directly without anything in between them (often called flatten in other languages).

auto joiner(RoR, Separator) (
  RoR r,
  Separator sep
);

auto joiner(RoR) (
  RoR r
)
if (isInputRange!RoR && isInputRange!(ElementType!RoR));

Parameters

NameDescription
r An input range of input ranges to be joined.
sep A forward range of element(s) to serve as separators in the joined range.

Returns

A range of elements in the joined range. This will be a bidirectional range if both outer and inner ranges of RoR are at least bidirectional ranges. Else if both outer and inner ranges of RoR are forward ranges, the returned range will be likewise. Otherwise it will be only an input range. The range bidirectionality is propagated if no separator is specified.

See also

std.range.chain, which chains a sequence of ranges with compatible elements into a single range.

Note

When both outer and inner ranges of RoR are bidirectional and the joiner is iterated from the back to the front, the separator will still be consumed from front to back, even if it is a bidirectional range too.

Example

import std.algorithm.comparison : equal;
import std.conv : text;

assert(["abc", "def"].joiner.equal("abcdef"));
assert(["Mary", "has", "a", "little", "lamb"]
    .joiner("...")
    .equal("Mary...has...a...little...lamb"));
assert(["", "abc"].joiner("xyz").equal("xyzabc"));
assert([""].joiner("xyz").equal(""));
assert(["", ""].joiner("xyz").equal("xyz"));

Example

import std.algorithm.comparison : equal;
import std.range : repeat;

assert([""].joiner.equal(""));
assert(["", ""].joiner.equal(""));
assert(["", "abc"].joiner.equal("abc"));
assert(["abc", ""].joiner.equal("abc"));
assert(["abc", "def"].joiner.equal("abcdef"));
assert(["Mary", "has", "a", "little", "lamb"].joiner.equal("Maryhasalittlelamb"));
assert("abc".repeat(3).joiner.equal("abcabcabc"));

Example

joiner allows in-place mutation! 

import std.algorithm.comparison : equal;
auto a = [ [1, 2, 3], [42, 43] ];
auto j = joiner(a);
j.front = 44;
writeln(a); // [[44, 2, 3], [42, 43]]
assert(equal(j, [44, 2, 3, 42, 43]));

Example

insert characters fully lazily into a string 

import std.algorithm.comparison : equal;
import std.range : chain, cycle, iota, only, retro, take, zip;
import std.format : format;

static immutable number = "12345678";
static immutable delimiter = ",";
auto formatted = number.retro
    .zip(3.iota.cycle.take(number.length))
    .map!(z => chain(z[0].only, z[1] == 2 ? delimiter : null))
    .joiner
    .retro;
static immutable expected = "12,345,678";
assert(formatted.equal(expected));

Example

joiner can be bidirectional 

import std.algorithm.comparison : equal;
import std.range : retro;

auto a = [[1, 2, 3], [4, 5]];
auto j = a.joiner;
j.back = 44;
writeln(a); // [[1, 2, 3], [4, 44]]
assert(equal(j.retro, [44, 4, 3, 2, 1]));

Authors

Andrei Alexandrescu

License

Boost License 1.0.