Question

class foo {
    public readonly int bar;
};
foo a = new foo() { bar = 123 };

error CS0191: A readonly field cannot be assigned to (except in a constructor or a variable initializer)

How can I assign bar in the object initializer above?

Can I initialize readonly members without having to write a custom constructor for every class/struct ?

Answer 1

foo a = new foo() { bar = 123 };

is transformed by the compiler to

foo temp = new foo();
temp.bar = 123;
foo a = temp;

As you can see, the assignment to bar is neither in the foo constructor nor a variable initializer.

So the answer is: you can’t.