9.5 Class variables

Class variables are defined using the var or const keywords.

class A
{
    var x
    const k = 10
}

The meaning of var and const follow from the general meaning described in the sections 7 Variables and 1.4 Variables.

var	May be written to multiple times
const	May be written to only once

const variable properties can be written to only once. The compiler uses a specific data flow analysis to determine if a const variable has been written to at the point of an assignment to that variable. Informally, the effect of this algorithm can be seen in the following error cases:

It is an error to assign to a const instance or static variable in a statement that is outside of the instance or static initializer, respectively.
It is an error to assign to a const variable more than once in a sequence of statements with no control flow branches.
It is an error to assign to a const variable in more than one parallel control flow branch if the branch conditions are not compile-time constant expressions, or if the value of those branch conditions allow for one or more of those branches to be executed more than once.

The default value of a class or instance variable is the value of undefined coerced to the type of the variable.

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