Slack 里的神奇 julia 用法

综合讨论区
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Slack 目前不付费无法查看历史消息，所以摘抄一些有趣的 Julia 用法。

在回复中更新

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Q: 如何指定一种 Int8 类型的字面量写法？

A: #general@kristofferc

julia> struct I8 end; const i8 = I8(); Base.:*(a::Integer, b::I8) = Int8(a)

julia> 2i8
2

julia> 2i8 |> typeof
Int8
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#random@harmen_stoppels：找到 @which 是在哪里定义的：

julia> @which @which @which
var"@which"(__source__::LineNumberNode, __module__::Module, ex0) in InteractiveUtils at C:\Users\a309\AppData\Local\julias\julia-1.7\share\julia\stdlib\v1.7\InteractiveUtils\src\macros.jl:200
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#general@DaveMacMahon：shell 里的 using

$ using Statistics
using: command not found

$ function using() { julia -i -e "using $@"; }

$ using Statistics
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.7.3 (2022-05-06)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> mean(1:10)
5.5
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5

来点 C 系语法

#random@mose:

do you miss from C the ability to index arrays as index[array] ? fear not, Julia’s got you covered:

julia> Base.getindex(n::Int, a::AbstractArray) = a[n]

julia> A = rand(3)
3-element Vector{Float64}:
 0.9089330803737465
 0.6795629112987226
 0.24067299343429482

julia> 2[A]
0.6795629112987226

julia> A[2]
0.6795629112987226

julia> struct Horror{T}
           A::T
           offset::Int
       end

julia> Base.:(*)(A::AbstractArray) = first(A)

julia> Base.:(+)(A::AbstractArray, n::Int) = Horror(A, n)

julia> Base.:(*)(H::Horror) = H.A[firstindex(H.A) + H.offset]

julia> A = rand(3)
3-element Vector{Float64}:
 0.9247879490627814
 0.559416394770332
 0.5540632603178985

julia> *(A)
0.9247879490627814

julia> *(A + 2)
0.5540632603178985
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