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# This file is a part of Julia. License is MIT: https://julialang.org/license
"""
SubString(s::AbstractString, i::Integer, j::Integer=lastindex(s))
SubString(s::AbstractString, r::UnitRange{<:Integer})
Like [`getindex`](@ref), but returns a view into the parent string `s`
within range `i:j` or `r` respectively instead of making a copy.
# Examples
```jldoctest
julia> SubString("abc", 1, 2)
"ab"
julia> SubString("abc", 1:2)
"ab"
julia> SubString("abc", 2)
"bc"
```
"""
struct SubString{T<:AbstractString} <: AbstractString
string::T
offset::Int
ncodeunits::Int
function SubString{T}(s::T, i::Int, j::Int) where T<:AbstractString
i ≤ j || return new(s, 0, 0)
@boundscheck begin
checkbounds(s, i:j)
@inbounds isvalid(s, i) || string_index_err(s, i)
@inbounds isvalid(s, j) || string_index_err(s, j)
end
return new(s, i-1, nextind(s,j)-i)
end
end
@propagate_inbounds SubString(s::T, i::Int, j::Int) where {T<:AbstractString} = SubString{T}(s, i, j)
@propagate_inbounds SubString(s::AbstractString, i::Integer, j::Integer=lastindex(s)) = SubString(s, Int(i), Int(j))
@propagate_inbounds SubString(s::AbstractString, r::UnitRange{<:Integer}) = SubString(s, first(r), last(r))
@propagate_inbounds function SubString(s::SubString, i::Int, j::Int)
@boundscheck i ≤ j && checkbounds(s, i:j)
SubString(s.string, s.offset+i, s.offset+j)
end
SubString(s::AbstractString) = SubString(s, 1, lastindex(s))
SubString{T}(s::T) where {T<:AbstractString} = SubString{T}(s, 1, lastindex(s))
convert(::Type{SubString{S}}, s::AbstractString) where {S<:AbstractString} =
SubString(convert(S, s))
convert(::Type{T}, s::T) where {T<:SubString} = s
String(s::SubString{String}) = unsafe_string(pointer(s.string, s.offset+1), s.ncodeunits)
ncodeunits(s::SubString) = s.ncodeunits
codeunit(s::SubString) = codeunit(s.string)
length(s::SubString) = length(s.string, s.offset+1, s.offset+s.ncodeunits)
function codeunit(s::SubString, i::Integer)
@boundscheck checkbounds(s, i)
@inbounds return codeunit(s.string, s.offset + i)
end
function iterate(s::SubString, i::Integer=firstindex(s))
i == ncodeunits(s)+1 && return nothing
@boundscheck checkbounds(s, i)
y = iterate(s.string, s.offset + i)
y === nothing && return nothing
c, i = y
return c, i - s.offset
end
function getindex(s::SubString, i::Integer)
@boundscheck checkbounds(s, i)
@inbounds return getindex(s.string, s.offset + i)
end
function isvalid(s::SubString, i::Integer)
ib = true
@boundscheck ib = checkbounds(Bool, s, i)
@inbounds return ib && isvalid(s.string, s.offset + i)
end
thisind(s::SubString{String}, i::Int) = _thisind_str(s, i)
nextind(s::SubString{String}, i::Int) = _nextind_str(s, i)
function cmp(a::SubString{String}, b::SubString{String})
na = sizeof(a)
nb = sizeof(b)
c = ccall(:memcmp, Int32, (Ptr{UInt8}, Ptr{UInt8}, UInt),
pointer(a), pointer(b), min(na, nb))
return c < 0 ? -1 : c > 0 ? +1 : cmp(na, nb)
end
# don't make unnecessary copies when passing substrings to C functions
cconvert(::Type{Ptr{UInt8}}, s::SubString{String}) = s
cconvert(::Type{Ptr{Int8}}, s::SubString{String}) = s
function unsafe_convert(::Type{Ptr{R}}, s::SubString{String}) where R<:Union{Int8, UInt8}
convert(Ptr{R}, pointer(s.string)) + s.offset
end
pointer(x::SubString{String}) = pointer(x.string) + x.offset
pointer(x::SubString{String}, i::Integer) = pointer(x.string) + x.offset + (i-1)
"""
reverse(s::AbstractString) -> AbstractString
Reverses a string. Technically, this function reverses the codepoints in a string and its
main utility is for reversed-order string processing, especially for reversed
regular-expression searches. See also [`reverseind`](@ref) to convert indices in `s` to
indices in `reverse(s)` and vice-versa, and `graphemes` from module `Unicode` to
operate on user-visible "characters" (graphemes) rather than codepoints.
See also [`Iterators.reverse`](@ref) for
reverse-order iteration without making a copy. Custom string types must implement the
`reverse` function themselves and should typically return a string with the same type
and encoding. If they return a string with a different encoding, they must also override
`reverseind` for that string type to satisfy `s[reverseind(s,i)] == reverse(s)[i]`.
# Examples
```jldoctest
julia> reverse("JuliaLang")
"gnaLailuJ"
julia> reverse("ax̂e") # combining characters can lead to surprising results
"êxa"
julia> using Unicode
julia> join(reverse(collect(graphemes("ax̂e")))) # reverses graphemes
"ex̂a"
```
"""
function reverse(s::Union{String,SubString{String}})::String
sprint(sizehint=sizeof(s)) do io
i, j = firstindex(s), lastindex(s)
while i ≤ j
c, j = s[j], prevind(s, j)
write(io, c)
end
end
end
string(a::String) = String(a)
string(a::SubString{String}) = String(a)
function string(a::Union{Char, String, SubString{String}}...)
n = 0
for v in a
if v isa Char
n += codelen(v)
else
n += sizeof(v)
end
end
out = _string_n(n)
offs = 1
for v in a
if v isa Char
x = bswap(reinterpret(UInt32, v))
for j in 1:codelen(v)
unsafe_store!(pointer(out, offs), x % UInt8)
offs += 1
x >>= 8
end
else
unsafe_copyto!(pointer(out,offs), pointer(v), sizeof(v))
offs += sizeof(v)
end
end
return out
end
function repeat(s::Union{String, SubString{String}}, r::Integer)
r < 0 && throw(ArgumentError("can't repeat a string $r times"))
r == 1 && return String(s)
n = sizeof(s)
out = _string_n(n*r)
if n == 1 # common case: repeating a single-byte string
@inbounds b = codeunit(s, 1)
ccall(:memset, Ptr{Cvoid}, (Ptr{UInt8}, Cint, Csize_t), out, b, r)
else
for i = 0:r-1
unsafe_copyto!(pointer(out, i*n+1), pointer(s), n)
end
end
return out
end
getindex(s::AbstractString, r::UnitRange{<:Integer}) = SubString(s, r)
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