我在我运行的程序中发现，某个函数包含多次循环，该函数第一次执行会花费大量时间并消耗大量内存，而第二次之后的执行都很迅速。（使用Python执行相同算法时不出现此问题。）
以下是两次执行@time报告：
START
9.900494 seconds (18.60 M allocations: 1.008 GiB, 1.57% gc time)
0.032444 seconds (35.94 k allocations: 1.553 MiB)
END
经过调查，函数花费的时间主要在被反复执行的以下语句：
check(Ari(o1, za, Ari(o2, zb, Ari(o3, zc, zd))), results)
如果我将这句改为
1
那么函数就可以很快运行，结果如下：
START
0.006238 seconds (9.00 k allocations: 892.812 KiB)
0.000589 seconds (9.00 k allocations: 892.484 KiB)
END
但是如果改为：
true ? 1 : check(Ari(o1, za, Ari(o2, zb, Ari(o3, zc, zd))), results)
那么还是会执行很长时间，即使冒号后的部分肯定不会执行：
START
6.606485 seconds (18.01 M allocations: 1007.268 MiB, 2.32% gc time)
0.001203 seconds (9.24 k allocations: 896.281 KiB)
END
所以我就很想不清楚，为什么这一句在第一次调用函数中执行很长时间并花费大量内存？而且，即使在它存在但肯定被忽略的情况下，依旧会花费时间并占用内存？
我接触Julia并不多久，难免有些疏漏，感谢大家帮助。
完整代码
revm(x,y)=y-x
struct Ari
o::Function # can be +,-,*,/,revm,\
x::Union{Ari,Real}
y::Union{Ari,Real}
end
AbstractAri = Union{Ari, Real}
function transfer(o::Function,x::AbstractAri,y::AbstractAri)
o==revm ? (-,y,x) :
o==(\) ? (/,y,x) :
(o,x,y)
end
function result(ins::Ari)::Union{Real,Nothing}
o, x, y=ins.o,Real(ins.x),Real(ins.y)
(o==(/) && y==0 || o==(\) && x==0) ? nothing :
(x==nothing || y==nothing) ? nothing :
o(x::Real, y::Real)
end
Real(ins::Ari) = result(ins::Ari)
isHigherThan(self::AbstractAri, other::AbstractAri)=false
isHigherThan(self::Ari, other::Ari)::Bool=self.o in (*,/,\) && other.o in (+,-,revm)
isSameClass(self::AbstractAri, other::AbstractAri)=false
isSameClass(self::Ari, other::Ari) = (self.o in (*,/,\)) == (other.o in (*,/,\))
function Base.string(ins::Ari)::String
o,x,y=transfer(ins.o,ins.x,ins.y)
part1, part2 = string.((x,y))
if isHigherThan(ins,x)
part1 = "($part1)"
end
if isHigherThan(ins,y)
part2 = "($part2)"
elseif isSameClass(ins,y) && o in (-, /)
part2 = "($part2)"
end
return "$(part1)$(o)$(part2)"
end
function Base.:(==)(self::Ari, other::Ari)::Bool
o1, x1, y1 = transfer(self.o,self.x,self.y)
o2, x2, y2 = transfer(other.o,other.x,other.y)
o1 == o2 && ((x1==x2)&&(y1==y2)||(o1 in (+, *) && x1==y2 && x2==y1))
end
function mess(f::Function, a::Int, b::Int, c::Int, d::Int)::Nothing
ct = [a,b,c,d]
for z1 = 1:4, z2 = 1:3
s = Array{Int8,1}([1,2,3,4])
za = ct[s[z1]]
deleteat!(s,z1)
u = copy(s)
zb = ct[u[z2]]
deleteat!(u,z2)
zc = ct[u[1]]
zd = ct[u[2]]
f(za::Int,zb::Int,zc::Int,zd::Int)
f(za::Int,zb::Int,zc::Int,zd::Int)
end
end
check(ins::Ari, results::Array{Ari,1}) = result(ins::Ari) == 24 && ins ∉ results ? push!(results, ins) : nothing; nothing
function solve(a::Real,b::Real,c::Real,d::Real)::Nothing
results = Array{Ari,1}()
os = (+,-,revm,*,/,\)
for o1 in os, o2 in os, o3 in os
mess(a,b,c,d) do za::Int,zb::Int,zc::Int,zd::Int
check(Ari(o1, za, Ari(o2, zb, Ari(o3, zc, zd))), results)
end
end
for o1 in (*,/,\), o2 in (*,/,\), o3 in (+,-,revm)
mess(a,b,c,d) do za::Int,zb::Int,zc::Int,zd::Int
check(Ari(o3, Ari(o1, za, zb), Ari(o2, zc, zd)), results)
end
end
if length(results)>0
for ins in results
println("$(string(ins)) = $(result(ins))")
end
else
println("No results.")
end
end
println("START")
@time solve(4,4,4,4)
println()
@time solve(4,4,4,4)
println("END")
