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Improved nextind and prevind #23805

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Oct 1, 2017
Merged

Improved nextind and prevind #23805

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ea7ecb2
improved prevind and nextind
bkamins Sep 23, 2017
1b72987
fix rebase conflicts
bkamins Sep 23, 2017
dd1d949
change i to j in loop
bkamins Sep 23, 2017
710a481
wrap tests in @testset
bkamins Sep 23, 2017
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3 changes: 3 additions & 0 deletions NEWS.md
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Original file line number Diff line number Diff line change
Expand Up @@ -231,6 +231,9 @@ This section lists changes that do not have deprecation warnings.
Library improvements
--------------------

* The functions `nextind` and `prevind` now accept `nchar` argument that indicates
number of characters to move ([#23805]).

* The functions `strip`, `lstrip` and `rstrip` now return `SubString` ([#22496]).

* The functions `strwidth` and `charwidth` have been merged into `textwidth`([#20816]).
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63 changes: 61 additions & 2 deletions base/strings/basic.jl
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Expand Up @@ -239,11 +239,23 @@ end
prevind(s::DirectIndexString, i::Integer) = Int(i)-1
nextind(s::DirectIndexString, i::Integer) = Int(i)+1

function prevind(s::DirectIndexString, i::Integer, nchar::Integer)
nchar > 0 || throw(ArgumentError("nchar must be greater than 0"))
Int(i)-nchar
end

function nextind(s::DirectIndexString, i::Integer, nchar::Integer)
nchar > 0 || throw(ArgumentError("nchar must be greater than 0"))
Int(i)+nchar
end


"""
prevind(str::AbstractString, i::Integer)
prevind(str::AbstractString, i::Integer, nchar::Integer=1)

Get the previous valid string index before `i`.
Returns a value less than `1` at the beginning of the string.
If the `nchar` argument is given the function goes back `nchar` characters.

# Examples
```jldoctest
Expand All @@ -252,6 +264,10 @@ julia> prevind("αβγdef", 3)

julia> prevind("αβγdef", 1)
0

julia> prevind("αβγdef", 3, 2)
0

```
"""
function prevind(s::AbstractString, i::Integer)
Expand All @@ -269,11 +285,32 @@ function prevind(s::AbstractString, i::Integer)
return 0 # out of range
end

function prevind(s::AbstractString, i::Integer, nchar::Integer)
nchar > 0 || throw(ArgumentError("nchar must be greater than 0"))
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Why not accept 0?

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Handling of 0:

  • requires separate logic (additional if)
  • is unclear what should be the result if i is not a proper byte index (if one calls prevind one expects to get a proper byte index in return - this is an important invariant of those functions in my opinion)

e = endof(s)
j = Int(i)
j < 1 && return 0
while nchar > 0
if j > e
j = e
else
j -= 1
while j >= 1 && !isvalid(s,j)
j -= 1
end
end
j < 1 && return 0
nchar -= 1
end
j
end

"""
nextind(str::AbstractString, i::Integer)
nextind(str::AbstractString, i::Integer, nchar::Integer=1)

Get the next valid string index after `i`.
Returns a value greater than `endof(str)` at or after the end of the string.
If the `nchar` argument is given the function goes forward `nchar` characters.

# Examples
```jldoctest
Expand All @@ -282,6 +319,9 @@ julia> str = "αβγdef";
julia> nextind(str, 1)
3

julia> nextind(str, 1, 2)
5

julia> endof(str)
9

Expand All @@ -305,6 +345,25 @@ function nextind(s::AbstractString, i::Integer)
next(s,e)[2] # out of range
end

function nextind(s::AbstractString, i::Integer, nchar::Integer)
nchar > 0 || throw(ArgumentError("nchar must be greater than 0"))
e = endof(s)
j = Int(i)
while nchar > 0
if j < 1
j = 1
else
j > e && return j + nchar
j == e && return next(s,e)[2] + nchar - 1
for j = j+1:e
isvalid(s,j) && break
end
end
nchar -= 1
end
j
end

checkbounds(s::AbstractString, i::Integer) = start(s) <= i <= endof(s) || throw(BoundsError(s, i))
checkbounds(s::AbstractString, r::AbstractRange{<:Integer}) = isempty(r) || (minimum(r) >= start(s) && maximum(r) <= endof(s)) || throw(BoundsError(s, r))
# The following will end up using a deprecated checkbounds, when the covariant parameter is not Integer
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38 changes: 38 additions & 0 deletions base/strings/string.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,25 @@ function prevind(s::String, i::Integer)
j
end

function prevind(s::String, i::Integer, nchar::Integer)
nchar > 0 || throw(ArgumentError("nchar must be greater than 0"))
j = Int(i)
e = sizeof(s)
while nchar > 0
if j > e
j = endof(s)
else
j -= 1
@inbounds while j > 0 && is_valid_continuation(codeunit(s,j))
j -= 1
end
end
nchar -= 1
j <= 0 && return j - nchar
end
j
end

function nextind(s::String, i::Integer)
j = Int(i)
if j < 1
Expand All @@ -120,6 +139,25 @@ function nextind(s::String, i::Integer)
j
end

function nextind(s::String, i::Integer, nchar::Integer)
nchar > 0 || throw(ArgumentError("nchar must be greater than 0"))
j = Int(i)
e = sizeof(s)
while nchar > 0
if j < 1
j = 1
else
j += 1
@inbounds while j <= e && is_valid_continuation(codeunit(s,j))
j += 1
end
end
nchar -= 1
j > e && return j + nchar
end
j
end

## checking UTF-8 & ACSII validity ##

byte_string_classify(data::Vector{UInt8}) =
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71 changes: 71 additions & 0 deletions test/strings/basic.jl
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Expand Up @@ -552,3 +552,74 @@ end
@test_throws ParseError parse("\"\\.\"")
@test_throws ParseError parse("\'\\.\'")
end

@testset "prevind and nextind" begin
let strs = Any["∀α>β:α+1>β", GenericString("∀α>β:α+1>β")]
for i in 1:2
@test prevind(strs[i], 1) == 0
@test prevind(strs[i], 1, 1) == 0
@test prevind(strs[i], 2) == 1
@test prevind(strs[i], 2, 1) == 1
@test prevind(strs[i], 4) == 1
@test prevind(strs[i], 4, 1) == 1
@test prevind(strs[i], 5) == 4
@test prevind(strs[i], 5, 1) == 4
@test prevind(strs[i], 5, 2) == 1
@test prevind(strs[i], 5, 3) == 0
@test prevind(strs[i], 15) == 14
@test prevind(strs[i], 15, 1) == 14
@test prevind(strs[i], 15, 2) == 13
@test prevind(strs[i], 15, 3) == 12
@test prevind(strs[i], 15, 4) == 10
@test prevind(strs[i], 15, 10) == 0
@test prevind(strs[i], 15, 9) == 1
@test prevind(strs[i], 15, 10) == 0
@test prevind(strs[i], 16) == 15
@test prevind(strs[i], 16, 1) == 15
@test prevind(strs[i], 16, 2) == 14
@test prevind(strs[i], 20) == 15
@test prevind(strs[i], 20, 1) == 15
@test prevind(strs[i], 20, 10) == 1
@test_throws ArgumentError prevind(strs[i], 20, 0)

@test nextind(strs[i], -1) == 1
@test nextind(strs[i], -1, 1) == 1
@test nextind(strs[i], 0, 2) == 4
@test nextind(strs[i], 0, 20) == 26
@test nextind(strs[i], 0, 10) == 15
@test nextind(strs[i], 1) == 4
@test nextind(strs[i], 1, 1) == 4
@test nextind(strs[i], 1, 2) == 6
@test nextind(strs[i], 1, 9) == 15
@test nextind(strs[i], 1, 10) == 17
@test nextind(strs[i], 2) == 4
@test nextind(strs[i], 2, 1) == 4
@test nextind(strs[i], 3) == 4
@test nextind(strs[i], 3, 1) == 4
@test nextind(strs[i], 4) == 6
@test nextind(strs[i], 4, 1) == 6
@test nextind(strs[i], 14) == 15
@test nextind(strs[i], 14, 1) == 15
@test nextind(strs[i], 15) == 17
@test nextind(strs[i], 15, 1) == 17
@test nextind(strs[i], 20) == 21
@test nextind(strs[i], 20, 1) == 21
@test_throws ArgumentError nextind(strs[i], 20, 0)

for x in -10:20
n = p = x
for j in 1:40
p = prevind(strs[i], p)
@test prevind(strs[i], x, j) == p
n = nextind(strs[i], n)
@test nextind(strs[i], x, j) == n
end
end
end
@test prevind(strs[1], -1) == -2
@test prevind(strs[1], -1, 1) == -2

@test prevind(strs[2], -1) == 0
@test prevind(strs[2], -1, 1) == 0
end
end