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Function std.algorithm.searching.countUntil

Counts elements in the given forward range until the given predicate is true for one of the given needles.

auto countUntil(alias pred, R, Rs...)(
  R haystack,
  Rs needles
)
if (isForwardRange!R && (Rs.length > 0) && (isForwardRange!(Rs[0]) == isInputRange!(Rs[0])) && allSatisfy!(canTestStartsWith!(pred, R), Rs));

ptrdiff_t countUntil(alias pred, R, N)(
  R haystack,
  N needle
)
if (isInputRange!R && is(typeof(binaryFun!pred(haystack.front, needle)) : bool));

ptrdiff_t countUntil(alias pred, R)(
  R haystack
)
if (isInputRange!R && is(typeof(unaryFun!pred(haystack.front)) : bool));

Parameters

NameDescription
pred The predicate for determining when to stop counting.
haystack The input range to be counted.
needles Either a single element, or a forward range of elements, to be evaluated in turn against each element in haystack under the given predicate.

Returns

The number of elements which must be popped from the front of haystack before reaching an element for which startsWith!pred(haystack, needles) is true. If startsWith!pred(haystack, needles) is not true for any element in haystack, then -1 is returned. If more than one needle is provided, countUntil will wrap the result in a tuple similar to Tuple!(ptrdiff_t, "steps", ptrdiff_t needle)

See Also

indexOf

Example

writeln(countUntil("hello world", "world")); // 6
writeln(countUntil("hello world", 'r')); // 8
writeln(countUntil("hello world", "programming")); // -1
writeln(countUntil("日本語", "本語")); // 1
writeln(countUntil("日本語", '語')); // 2
writeln(countUntil("日本語", "五")); // -1
writeln(countUntil("日本語", '五')); // -1
writeln(countUntil([0, 7, 12, 22, 9], [12, 22])); // 2
writeln(countUntil([0, 7, 12, 22, 9], 9)); // 4
writeln(countUntil!"a > b"([0, 7, 12, 22, 9], 20)); // 3

// supports multiple needles
auto res = "...hello".countUntil("ha", "he");
writeln(res.steps); // 3
writeln(res.needle); // 1

// returns -1 if no needle was found
res = "hello".countUntil("ha", "hu");
writeln(res.steps); // -1
writeln(res.needle); // -1

Example

import std.ascii : isDigit;
import std.uni : isWhite;

writeln(countUntil!(isWhite)("hello world")); // 5
writeln(countUntil!(isDigit)("hello world")); // -1
writeln(countUntil!"a > 20"([0, 7, 12, 22, 9])); // 3

Authors

Andrei Alexandrescu

License

Boost License 1.0.