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version 2.080.0

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Function std.utf.strideBack

Calculate the length of the UTF sequence ending one code unit before index in str.

uint strideBack(S) (
  auto ref S str,
  size_t index
)
if (is(S : const(char[])) || isRandomAccessRange!S && is(Unqual!(ElementType!S) == char));

uint strideBack(S) (
  auto ref S str
)
if (is(S : const(char[])) || isRandomAccessRange!S && hasLength!S && is(Unqual!(ElementType!S) == char));

uint strideBack(S) (
  auto ref S str
)
if (isBidirectionalRange!S && is(Unqual!(ElementType!S) == char) && !isRandomAccessRange!S);

uint strideBack(S) (
  auto ref S str,
  size_t index
)
if (is(S : const(wchar[])) || isRandomAccessRange!S && is(Unqual!(ElementType!S) == wchar));

uint strideBack(S) (
  auto ref S str
)
if (is(S : const(wchar[])) || isBidirectionalRange!S && is(Unqual!(ElementType!S) == wchar));

uint strideBack(S) (
  auto ref S str,
  size_t index
)
if (isRandomAccessRange!S && is(Unqual!(ElementEncodingType!S) == dchar));

uint strideBack(S) (
  auto ref S str
)
if (isBidirectionalRange!S && is(Unqual!(ElementEncodingType!S) == dchar));

Parameters

NameDescription
str bidirectional range of UTF code units. Must be random access if index is passed
index index one past end of UTF sequence (default: str.length)

Returns

The number of code units in the UTF sequence. For UTF-8, this is a value between 1 and 4 (as per RFC 3629, section 3). For UTF-16, it is either 1 or 2. For UTF-32, it is always 1.

Throws

May throw a UTFException if str[index] is not one past the end of a valid UTF sequence.

Note

strideBack will only analyze the element at str[index - 1] element. It will not fully verify the validity of the UTF sequence, nor even verify the presence of the sequence: it will not actually guarantee that strideBack(str, index) <= index.

Example

writeln("a".strideBack); // 1
writeln("λ".strideBack); // 2
writeln("aλ".strideBack); // 2
writeln("aλ".strideBack(1)); // 1
writeln("𐐷".strideBack); // 4

Authors

Walter Bright and Jonathan M Davis

License

Boost License 1.0.