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Make startswith work with IO objects #43055

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merged 9 commits into from
Feb 14, 2023
Merged

Make startswith work with IO objects #43055

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0dd0cd9
startswith for io objects
ArunS-tack Nov 12, 2021
104a5b3
Update base/strings/util.jl
ArunS-tack Mar 24, 2022
ea555ed
Update basic.jl
ArunS-tack Dec 18, 2022
edbf385
Merge branch 'master' into iosw
ArunS-tack Dec 18, 2022
f64cb06
Merge branch 'JuliaLang:master' into iosw
ArunS-tack Dec 26, 2022
7df36be
news
ArunS-tack Dec 26, 2022
942f4a9
Merge branch 'master' into iosw
KristofferC Feb 13, 2023
5d4123d
add cross-reference in peek
stevengj Feb 13, 2023
22f5b2e
Update base/strings/util.jl
stevengj Feb 13, 2023
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19 changes: 19 additions & 0 deletions base/strings/util.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,25 @@ function startswith(a::Union{String, SubString{String}},
end
end

"""
startswith(io::IO, prefix::Union{AbstractString,Base.Chars})

Check if an `IO` object starts with a prefix.
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"""
function Base.startswith(io::IO, prefix::Base.Chars)
mark(io)
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@stevengj stevengj Feb 13, 2023 •
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Seems worth it to optimize the common case of an ASCII char, especially since a stream may conceivably support peek but not mark/reset.

Suggested change
mark(io)
prefix isa AbstractChar && prefix ≤ '\x7f' && return peek(io) == prefix % UInt8
mark(io)

c = read(io, Char)
reset(io)
return c in prefix
end
function Base.startswith(io::IO, prefix::Union{String,SubString{String}})
mark(io)
s = read(io, ncodeunits(prefix))
reset(io)
return s == codeunits(prefix)
end
Base.startswith(io::IO, prefix::AbstractString) = startswith(io, String(prefix))

function endswith(a::Union{String, SubString{String}},
b::Union{String, SubString{String}})
cub = ncodeunits(b)
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3 changes: 3 additions & 0 deletions test/strings/basic.jl
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Expand Up @@ -164,6 +164,9 @@ end
@test endswith(y)(y)
@test endswith(z, z)
@test endswith(z)(z)
#40616 startswith for IO objects
io = IOBuffer("JuliaLang")
@test startswith(io, "Julia")
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end

@testset "SubStrings and Views" begin
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