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Function std.algorithm.searching.findSplit

These functions find the first occurrence of needle in haystack and then split haystack as follows.

auto findSplit(alias pred, R1, R2)(
  R1 haystack,
  R2 needle
)
if (isForwardRange!R1 && isForwardRange!R2);

findSplit returns a tuple result containing three ranges. If needle was not found, result[0] comprehends haystack entirely and result[1] and result[2] are empty. findSplitBefore returns a tuple result containing two ranges.
  • result[0] is the portion of haystack before needle
  • result[1] is the balance of haystack starting with the match.
If needle was not found, result[0] comprehends haystack entirely and result[1] is empty. findSplitAfter returns a tuple result containing two ranges.
  • result[0] is the portion of haystack up to and including the match
  • result[1] is the balance of haystack starting after the match.
If needle was not found, result[0] is empty and result[1] is haystack.

In all cases, the concatenation of the returned ranges spans the entire haystack. If haystack is a random-access range, all three components of the tuple have the same type as haystack. Otherwise, haystack must be a forward range and the type of result[0] (and result[1] for findSplit) is the same as the result of std.range.takeExactly. For more information about pred see find.

Parameters

NameDescription
pred Predicate to compare 2 elements.
haystack The forward range to search.
needle The forward range to look for.

Returns

A sub-type of Tuple of the split portions of haystack (see above for details). This sub-type of Tuple defines opCast!bool, which returns true when the separating needle was found and false otherwise.

See Also

find

Example

Returning a subtype of Tuple enables the following convenient idiom: 

// findSplit returns a triplet
if (auto split = "dlang-rocks".findSplit("-"))
{
    writeln(split[0]); // "dlang"
    writeln(split[1]); // "-"
    writeln(split[2]); // "rocks"
}
else assert(0);

// findSplitBefore returns 2 ranges
if (const split = [2, 3, 2, 3, 4, 1].findSplitBefore!"a > b"([2, 2]))
{
    writeln(split[0]); // [2, 3, 2]
    // [3, 4] each greater than [2, 2]
    writeln(split[1]); // [3, 4, 1]
}
else assert(0);

Example

import std.range.primitives : empty;

auto a = "Carl Sagan Memorial Station";
auto r = findSplit(a, "Velikovsky");
import std.typecons : isTuple;
static assert(isTuple!(typeof(r.asTuple)));
static assert(isTuple!(typeof(r)));
assert(!r);
writeln(r[0]); // a
assert(r[1].empty);
assert(r[2].empty);
r = findSplit(a, " ");
writeln(r[0]); // "Carl"
writeln(r[1]); // " "
writeln(r[2]); // "Sagan Memorial Station"
if (const r1 = findSplitBefore(a, "Sagan"))
{
    assert(r1);
    writeln(r1[0]); // "Carl "
    writeln(r1[1]); // "Sagan Memorial Station"
}
if (const r2 = findSplitAfter(a, "Sagan"))
{
    assert(r2);
    writeln(r2[0]); // "Carl Sagan"
    writeln(r2[1]); // " Memorial Station"
}

Example

Use std.range.only to find single elements: 

import std.range : only;
writeln([1, 2, 3, 4].findSplitBefore(only(3))[0]); // [1, 2]

Authors

Andrei Alexandrescu

License

Boost License 1.0.