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Add a more efficient implementation for String(::ReinterpretArray) #58438

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Add a more efficient implementation for String(::ReinterpretArray) #58438

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a76df84
Add a more efficient implementation for String(::ReinterpretArray)
lntricate1 May 16, 2025
6007ffa
Fix issue pointed out by jakobnissen
lntricate1 May 19, 2025
dff029d
Add tests
lntricate1 May 20, 2025
f2ea9b8
Forgot to refill v
lntricate1 May 20, 2025
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10 changes: 10 additions & 0 deletions base/strings/string.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,16 @@ function String(v::Vector{UInt8})
setfield!(v, :ref, memoryref(Memory{UInt8}()))
return str
end
function String(v::ReinterpretArray{UInt8, 1, S, Vector{S}, IsReshaped}) where {S, IsReshaped}
len = length(v)
len == 0 && return ""
return ccall(:jl_pchar_to_string, Ref{String}, (Ptr{S}, Int), v.parent.ref, len)
end
function String(v::ReinterpretArray{UInt8, 1, S, Memory{S}, IsReshaped}) where {S, IsReshaped}
len = length(v)
len == 0 && return ""
return ccall(:jl_pchar_to_string, Ref{String}, (Ptr{S}, Int), v.parent.ptr, len)
end

"Create a string re-using the memory, if possible.
Mutating or reading the memory after calling this function is undefined behaviour."
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8 changes: 8 additions & 0 deletions test/strings/basic.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,14 @@ using Random
@test String("abc!") == "abc!"
@test String(0x61:0x63) == "abc"

v = [0x61,0x62,0x63,0x21]
v32 = copy(reinterpret(UInt32, v))
@test String(reinterpret(UInt8, v32)) == "abc!" && !isempty(v32)
@test 1 == @allocations String(reinterpret(UInt8, v32))
m32 = v32.ref.mem
@test String(reinterpret(UInt8, m32)) == "abc!" && !isempty(m32)
@test 1 == @allocations String(reinterpret(UInt8, m32))

# Check that resizing empty source vector does not corrupt string
b = IOBuffer()
@inferred write(b, "ab")
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