Dfyjkt

I know that using global variable is not good practice and programmers should avoid it when possible.

func foo(a *A) func() *A 
 return func() *A 
 return a
 

If I call foo_closure inside another function bar it would mean that output of bar will not depend on its input arguments and bar cannot be pure function.

Now I cannot see a difference between accessing a *A variable by closure or by global variable. In both cases they make an output unpredictable.
Can closure be considered an evil thing as global variable?

P.S
Other functions can also call foo_closure and mutate its fields.

The output is unpredictable with a global variable if "something else" besides your function yourfunc changes the global variable's value in between the calls to yourfunc.

But if the variable var is enclosed inside a closure and is accessible only to yourfunc, nothing else has access to it so can't change it so yourfunc's output becomes entirely predictable by the arguments to yourfunc and by yourfunc's actions (like, mutating the enclosed variable var, which can only be done from inside yourfunc).

Which increases safety and purity, which is the whole point to having closures in the first place.

The value of a function depends on its environment, comprised of its arguments, and the enclosed variables.

Another use of closures is when the enclosed environment is shared between several functions, so that only those functions can access and alter the enclosed variables' values.

Having variables global unnecessarily, litters the global name space and makes them liable for erroneous access.