今天温习c语言时，突然发现Julia好像没有switch和case，文档里流程控制那块没有提到这个，难道是我看走眼了？？
Match.jl 貌似19就没更新了。
pattern match 当然用 MLStyle.jl 啦
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module CSwitch
export @cswitch
# inspired by dcjones's Switch.jl
macro cswitch(constexpr, body)
case2label = Dict{Any,Symbol}()
flow = Expr(:block)
end_label = gensym("end")
default_label = end_label
for arg in body.args
if Meta.isexpr(arg, :macrocall) && arg.args[1] == Symbol("@case")
label = gensym("case")
case2label[arg.args[3]] = label
labelexpr = Expr(:symboliclabel, label)
push!(flow.args, labelexpr)
elseif Meta.isexpr(arg, :macrocall) && arg.args[1] == Symbol("@default")
default_label = gensym("default")
labelexpr = Expr(:symboliclabel, default_label)
push!(flow.args, labelexpr)
elseif arg == Expr(:break)
labelexpr = Expr(:symbolicgoto, end_label)
push!(flow.args, labelexpr)
else
push!(flow.args, arg)
end
end
push!(flow.args, Expr(:symboliclabel, end_label))
jumptable = Expr(:block)
for (case, label) in case2label
condition = Expr(:call, :(==), constexpr, case)
push!(jumptable.args, Expr(:if, condition, Expr(:symbolicgoto, label)))
end
push!(jumptable.args[end].args, Expr(:symbolicgoto, default_label))
return esc(Expr(:block, jumptable, flow))
end
end # module
@enum test t=1 f=2
tester = t
@cswitch tester begin
@case t
x = 1
break
@case f
x = 2
break
end
x == 1
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多分派可以代替一部分switch的功能
随手写了一段，仅供娱乐……
julia> json(x)=string(x)
json (generic function with 1 method)
julia> json(x::String)=begin io=IOBuffer();show(io,x);String(take!(io)) end
json (generic function with 2 methods)
julia> json(x::Array)="["*join(map(json,x),",")*"]"
json (generic function with 3 methods)
julia> json(x::Dict)="{"*join(map(((k,v),)->json(string(k))*":"*json(v),collect(pairs(x))),",")*"}"
json (generic function with 4 methods)
julia> a=Dict(:a=>1,:b=>[2,3],:c=>Dict(:x=>4.0,:y=>"5"))
Dict{Symbol,Any} with 3 entries:
:a => 1
:b => [2, 3]
:c => Dict{Symbol,Any}(:y=>"5",:x=>4.0)
julia> json(a)
"{\"a\":1,\"b\":[2,3],\"c\":{\"y\":\"5\",\"x\":4.0}}"
格式化一下
{
"a" : 1,
"b" : [ 2, 3 ],
"c" : {
"y" : "5",
"x" : 4.0
}
}