Re: Pass a serial port as user data in a GTK callback handler?

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 14-02-16 01:32 , hreba wrote:
> Hi,
> 
> I am new to Ada and still overwhelmed by the complexity of the language.
> 
> My actual programming exercise has a GTK GUI, and I want a callback
> handler to communicate through a serial port, so I need to pass the port
> in my user data, which must be of
> 
>    type User_Type (<>) is private;
> 
> which means it must be nonlimited.
> 
> But GNAT.Serial_Communications.Serial_Port is limited:
> 
>    type Serial_Port is new Ada.Streams.Root_Stream_Type with private;
>    type Root_Stream_Type is abstract tagged limited private;
> 
> I tried to pass a reference to the port, and it must be an "access all"
> (because it is not allocated by my, but a preexisting variable (hardware
> resource), as I understand it):

On my machine (Win 7), the type Serial_Port is declared in
GNAT.Serial_Communications by deriving from
Ada.Streams.Root_Stream_Type, adding a component which refers AIUI to a
Windows "handle". This is definitely a SW object; the HW resource is
hidden beind Windows.

On some bare-machine GNAT port, Serial_Port might be closer to the HW,
but it is no doubt still a stream class, so it will not itself be mapped
to some HW register. It might contain the address of (i.e. a reference
to) a HW register.

Therefore, you should be able to create your own Serial_Port objects on
the stack, on the heap, or statically.

>    port: access all GNAT.Serial_Communications.Serial_Port;
> 
> But then I get an error message
> 
>    "all" is not permitted for anonymous access types.
> 
> Is there a solution?

Give the type a name so that it isn't "anonymous":

   type Port_Ref is access all GNAT.Serial_Communications.Serial_Port;

   port : Port_Ref;

Also remember to mark the actual Serial_Port object as "aliased" so that
you can take its 'Access.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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