Additionally, specifying that the RValue "[1,2]" has mutability is meaningless. The expression "[1,2]" is represented as a constant until it is stored in a variable (it should be represented in the MACH-O constant data section). It is the variable which has the concept of mutability.
The proposal is similar to proposing the following declaration in C:
"int i = const 1;"
Which is meaningless, because the '1' can never be not-const