c# - Casting int[] to object[]

Question

I encountered with question: why it's impossible cast int[] to object[] , e.g. object[] o = new int[] { 0, 1, 2 };

Meanwhile I can cast to just object and back to int[].

I'll be glad to hear deep answer.

Answer 1

Directly from the docs:

Array covariance specifically does not extend to arrays of value-types. For example, no conversion exists that permits an int[] to be treated as an object[].

An array of ints or any other value-type is not an array of objects. Value types have different storage characteristics to those of reference types. An array of (reference type) objects holds a list of object references (with the objects themselves living in the heap), so the slots will always be a constant width. Value types, on the other hand, store their value directly in the array, so the slots might be any width. This makes a conversion between the two meaningless.

It's a little confusing because even though value-types are derived from System.Object, they behave very differently to reference types, and object-like behaviour of value types (e.g. boxing) is only possible through magical handling of them by the compiler and runtime, and it doesn't extend to arrays.

As a side note, casting arrays is a well dodgy practice. I wouldn't do it.