Incorrect "assignment" behavior (XBase++) about xsharppublic HOT 10 OPEN

We will change this and implement it just like C# does: only assignments in the constructor will be allowed

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If you implement this as in C#, then a lot of legacy Alaska code will not compile on XSharp. We planned to replace the readonly (if there are any difficulties with it) with the assignment hidden|protected.

from xsharppublic.

If you implement this as in C#, then a lot of legacy Alaska code will not compile on XSharp. We planned to replace the readonly (if there are any difficulties with it) with the assignment hidden|protected.

Why would that not work?

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Because at the moment class fields marked with readonly can only be assigned inside a constructor, but not inside methods of the same class, although Alaska allows this.

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This ticket shows exactly this difference in the behavior of the keyword readonly

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Ok, so the readonly modifier describes a field that acts like a property in C# with public get, private set.
The easiest way to implement this would be an auto property with public get private set. Would that be OK?

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From Alaska documentation about the readonly

The option READONLY limits write access for an instance variable. The assignment of a value to an instance variable declared READONLY is only permitted within the source code of methods. If the instance variable has global visibility (visibility attribute EXPORTED:), an assignment can be made within methods of the class and its subclasses. If the visibility attribute is PROTECTED:, READONLY limits the assignment to the methods of the declared class.

That is, depending on the visibility of the field, the assignment area will also change

from xsharppublic.

DotNet does not have a different visibility for GET/SET for fields (class variables)
So we will have to translate

exported:
var nNumber assignment hidden

into an auto property with a different visibility for the setter and getter

in X# Core class syntax that would become

class Example
    public property nNumber as USUAL AUTO GET HIDDEN SET
    constructor(nNumber)
        ::nNumber := nNumber
    METHOD SetNumber(nNumber)
        ::nNumber := nNumber
        RETURN SELF
end class

and that will result in a runtime error when assigning the number like in this code

o:nNumber := 10

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Perfect solution. Then the same solution can be applied for the keyword readonly #1490.

Yes, this assignment o:nNumber := 10 ends in a runtime error in alaska.

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Robert, this solution does not fully work as expected. There is neither a compile-time nor a runtime error.

The compiler throws no error because the member access is late-bound and the compiler is happy to translate o:nNumber := 10 to an IVarPut() call.

No runtime error is thrown either (!!!), although the assignment itself is not executed. So, the output of the sample becomes:

4
15

Also, note that since it is now a property the address-of operator won't work on it (if that's applicable). It should work when passed as a ref-argument, though.

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