What is the use of a constant union object?

Question

If I make a const union object (e.g in code below ), then no member assignment can be done in that. So is there any use of making a const union object, in any case ?

union un
{
    int i;
    float f;
    char c;
};
const union un a; 
/// ! a.i = 10; error.

Answer 1

You can still initialize the union as follows:

const union un a = { .i = 100 }; 

then use it in your code.

Answer 2

You can still assign it at declaration, for instance like this:

const union un a = {0};

Update: that notation sets the first of the union members.