Does Julia Need a C++ style `static` keyword?

Internals & Design
6

You can use an inner constructor (eg in the example below, with validation):

let counter = 0
    global get_counter() = counter

    struct Foo
        x::Int
        function Foo(x)
            x > 0 || error("invalid x")
            counter += 1
            new(x)
        end
    end
end

which works like this (note counter is only incremented when you create a valid Foo):

julia> get_counter()
0

julia> Foo(1)
Foo(1)

julia> get_counter()
1

julia> Foo(-1)
ERROR: invalid x
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] Foo(::Int64) at /tmp/foo.jl:7
 [3] top-level scope at REPL[41]:1

julia> get_counter()
1

That said, global mutable state is difficult to reason about and may preclude some compiler optimizations, so it is generally avoided in Julia. Instead of porting code in C++ style, I would recommend finding another solution.

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