ReversedStrings

provides a fast lazy reverse AbstractString interface implementation.

julia> using ReversedStrings

julia> using BenchmarkTools

julia> @btime reverse("JuliaCon")
  28.694 ns (1 allocation: 32 bytes)
"noCailuJ"

julia> @btime reversed("JuliaCon")
  3.167 ns (0 allocations: 0 bytes)
"noCailuJ"

julia> @btime reverse(reverse("JuliaCon"))
  58.530 ns (2 allocations: 64 bytes)
"JuliaCon"

julia> @btime reversed(reversed("JuliaCon"))
  3.734 ns (0 allocations: 0 bytes)
"JuliaCon"

The package is used in CombinedParsers.jl for lookbehind parsers.

ReversedStrings.ReversedString — Type

ReversedString{V}<:AbstractString

Lazy reversed V struct holding representation and caching lastindex.

source

ReversedStrings.reversed — Function

reversed(x::AbstractString)

A lazy implementation of Base.reverse for Strings.

source

ReversedStrings.reverse_index — Function

reverse_index(x::ReversedString,i)

Return corresponding index in unreversed String x.lastindex-i+1.

source

reverse_index(x::AbstractString,i)

Return original index i.

source

Base.firstindex — Function

Base.firstindex(x::ReversedString)

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Base.lastindex — Function

Base.lastindex(x::ReversedString)

cached x.lastindex.

source

Base.length — Function

Base.length(x::ReversedString)

length(x.representation)

source

Base.ncodeunits — Function

Base.ncodeunits(x::ReversedString)

ncodeunits(x.representation)

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Base.thisind — Function

Base.thisind(x::ReversedString,i::Integer)

reverse_index(thisind(x.representation,reverse_index(x,i))).

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Base.prevind — Function

Base.prevind(x::ReversedString,i[,n=1])

reverse_index(prevind(x.representation,reverse_index(x,i))[,n]).

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Base.nextind — Function

Base.nextind(x::ReversedString,i[,n=1])

reverse_index(nextind(x.representation,reverse_index(x,i))[,n]).

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Base.iterate — Function

Base.iterate(x::ReversedString[, state])

Iterate lazy reversed string.

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Base.getindex — Function

Base.getindex(x::ReversedString,is::UnitRange{<:Integer})

ReversedString of getindex on representation.

Note

getindex is creating a new String representation. See SubString

source

Base.getindex(x::ReversedString,i::Integer)

getindex(x.representation,reverse_index(x,i)).

source

Base.codeunit — Function

Base.ncodeunits(x::ReversedString)

codeunit(x.representation,reverse_index(x,i)).

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Base.isvalid — Function

Base.isvalid(x::ReversedString,i::Int)

isvalid(x.representation,reverse_index(x,i)).

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Base.SubString — Type

Base.SubString(x::ReversedString,start::Int,stop::Int)

Create a reversed SubString using reverse_index.

source

References:

https://discourse.julialang.org/t/what-is-the-interface-of-abstractstring/8937