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structjuliagloballocal

Why mutable struct cannot be defined inside a function in Julia

Why mutable struct cannot be defined inside a function in Julia?

function test()
    mutable struct ABC
        x
        y
        z
        a
    end 
end

throws error:

ERROR: LoadError: syntax: "struct" expression not at top level

But if the struct is global that is outside the function and accessed inside function, the code works fine.

Solution

  • Struct types must be defined at top-level (i.e. in the "module scope"), as the error suggest, and you can not define function-local structs like in your example.

    If you really don't want to define the struct type in a module, then you can use a NamedTuple, which can sometimes take the place of an "anonymous struct type". Example:

    function test()
    nt = (x = 1, y = 2, z = 3, a = "hello")
    # ...
end