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Function std.algorithm.searching.findSplitBefore

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

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

findSplit returns a tuple result containing three ranges. result[0] is the portion of haystack before needle, result[1] is the portion of haystack that matches needle, and result[2] is the portion of haystack after the match. 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, and 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, and 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] is the same as std.range.takeExactly.

Parameters

NameDescription
pred Predicate to use for comparing needle against haystack.
haystack The range to search.
needle What to look for.

Returns

A sub-type of Tuple!() of the split portions of haystack (see above for details). This sub-type of Tuple!() has opCast defined for bool. This opCast returns true when the separating needle was found (!result[1].empty) 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[2]); // "rocks"

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"
auto r1 = findSplitBefore(a, "Sagan");
assert(r1);
writeln(r1[0]); // "Carl "
writeln(r1[1]); // "Sagan Memorial Station"
auto 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.