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utf8.offset returns also final position of character

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'utf8.offset' returns two values: the initial and the final position
of the given character.
This commit is contained in:
Roberto Ierusalimschy
2024-05-27 11:29:39 -03:00
parent cbdf4969ec
commit 814213b65f
3 changed files with 55 additions and 31 deletions
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manual/manual.of
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@@ -7958,21 +7958,27 @@ returns @fail plus the position of the first invalid byte.
@LibEntry{utf8.offset (s, n [, i])|
Returns the position (in bytes) where the encoding of the
@id{n}-th character of @id{s}
(counting from position @id{i}) starts.
Returns the the position of the @id{n}-th character of @id{s}
(counting from byte position @id{i}) as two integers:
The index (in bytes) where its encoding starts and the
index (in bytes) where it ends.
If the specified character is right after the end of @id{s},
the function behaves as if there was a @Char{\0} there.
If the specified character is neither in the subject
nor right after its end,
the function returns @fail.
A negative @id{n} gets characters before position @id{i}.
The default for @id{i} is 1 when @id{n} is non-negative
and @T{#s + 1} otherwise,
so that @T{utf8.offset(s, -n)} gets the offset of the
@id{n}-th character from the end of the string.
If the specified character is neither in the subject
nor right after its end,
the function returns @fail.
As a special case,
when @id{n} is 0 the function returns the start of the encoding
of the character that contains the @id{i}-th byte of @id{s}.
when @id{n} is 0 the function returns the start and end
of the encoding of the character that contains the
@id{i}-th byte of @id{s}.
This function assumes that @id{s} is a valid UTF-8 string.