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Compiler Warning (future error) AL0920

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The method '{0}' cannot be used as the implementation for the interface method '{1}' because it is not public.

Important

This warning will become an error with Business Central 2027 release wave 1.

Description

Interface implementations must be publicly accessible because interfaces can be invoked across module boundaries. Non-public methods will not be dispatched correctly at runtime.

Remarks

This diagnostic is currently a warning but will become an error in a future version (runtime 17.0 / Spring 2027). Interface methods are called through an interface variable, which can be passed across module boundaries. If the implementing method is local or internal, the runtime cannot always dispatch the call correctly.

Important

This warning will become error AL0921 in a future runtime version. Update your code now to avoid a breaking change.

How to fix it

Change the accessibility of the implementing method to public by removing the local or internal access modifier.

Example of code that triggers AL0920

interface IMyInterface
{
    procedure Calculate(): Integer;
}

codeunit 50100 MyCodeunit implements IMyInterface
{
    // This triggers AL0920 because the method is local,
    // but it implements an interface method that must be public.
    internal procedure Calculate(): Integer;
    begin
        exit(42);
    end;
}

Example of how to fix it

Make the implementing method public.

interface IMyInterface
{
    procedure Calculate(): Integer;
}

codeunit 50100 MyCodeunit implements IMyInterface
{
    procedure Calculate(): Integer;
    begin
        exit(42);
    end;
}

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Compiler Error AL0921

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