在Julia中定义常量全局变量

Question

在Julia中,将变量const定义为和定义变量之间的区别是const global什么？考虑以下示例,如果我更改const global为有const什么区别？

#set number of cores
number_cores=7;
addprocs(number_cores)

#include necessary functions
@everywhere include("$(pwd())\\lib.jl");

const global n = 2; # number of observables
const global k = nVAR + 2*n-1; # number of states
const global m = k*q;

pmap(a->parallel_un(a,n,k,m),1:7)

Answer 1

有两种情况:

1. 如果你是在全球范围内则const和const global是相同的;
2. 如果您处于全局以外的某个范围,则const在Julia 0.7中不推荐使用,并且使用const global是可接受的并定义全局常量.

这是一个示例会话:

               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.7.0-DEV.3404 (2018-01-14 21:52 UTC)
 _/ |\__'_|_|_|\__'_|  |  Commit d569a2923c* (30 days old master)
|__/                   |  x86_64-w64-mingw32

julia> f() = (const global x = 1)
f (generic function with 1 method)

julia> f()
1

julia> x = "a"
ERROR: invalid redefinition of constant x

julia> g() = (const global y = 1)
g (generic function with 1 method)

julia> y = 1
1

julia> g()
ERROR: cannot declare y constant; it already has a value
Stacktrace:
 [1] g() at .\REPL[4]:1
 [2] top-level scope