julia

9eb27705 - add sizehint! for `first` and make append!/prepend! safer (#51903)

add sizehint! for `first` and make append!/prepend! safer (#51903) First we add an optional API parameter for `sizehint!` that controls whether it is for `push!` (default) or `pushfirst!`. Secondly, we make the offset zero when using `sizehint!` to shrink an array from the end, or the trailing size zero when using it to shring from the beginning. Then we replace the prior implementations of `prepend!` and `append!` with ones that are safe even if the iterator changes length during the operation or if convert fails. The result of `prepend!` may be in an undefined order (because of the `reverse!` call) in the presence of concurrent modifications or errors, but at least all of the elements will be present and valid afterwards. Replaces and closes #49905 Replaces and closes #47391 Fixes #15868 Benchmarks show that repeated `push!` performance (with sizehint) is nearly equivalent to the old append performance: ``` julia> @benchmark append!(x, 1:1000) setup=x=Vector{Float64}(undef,0) BenchmarkTools.Trial: 10000 samples with 10 evaluations. Range (min … max): 1.027 μs … 72.871 μs ┊ GC (min … max): 0.00% … 94.57% Time (median): 1.465 μs ┊ GC (median): 0.00% Time (mean ± σ): 1.663 μs ± 1.832 μs ┊ GC (mean ± σ): 6.20% ± 5.67% ▂▃▅▆█▇▇▆▄▂▁ ▂▁▁▂▂▂▂▃▄▅▇█████████████▇▆▅▅▅▅▅▅▄▅▄▅▅▅▆▇███▆▅▄▃▃▂▂▂▂▂▂▂▂▂▂ ▄ 1.03 μs Histogram: frequency by time 2.31 μs < Memory estimate: 19.69 KiB, allocs estimate: 0. julia> @benchmark append!(x, 1:1000) setup=x=Vector{Int}(undef,0) BenchmarkTools.Trial: 10000 samples with 10 evaluations. Range (min … max): 851.900 ns … 76.757 μs ┊ GC (min … max): 0.00% … 91.59% Time (median): 1.181 μs ┊ GC (median): 0.00% Time (mean ± σ): 1.543 μs ± 1.972 μs ┊ GC (mean ± σ): 6.75% ± 5.75% ▆█▇▃ ▂▃██████▇▅▅▄▅▅▃▂▂▂▃▃▃▂▃▃▃▂▂▂▂▂▁▂▁▂▁▂▂▂▁▁▂▂▁▁▁▁▁▁▁▂▂▂▃▃▃▃▂▂▂▂ ▃ 852 ns Histogram: frequency by time 4.07 μs < Memory estimate: 19.69 KiB, allocs estimate: 0. ``` Co-authored-by: Sukera <Seelengrab@users.noreply.github.com> Co-authored-by: MasonProtter <mason.protter@icloud.com>