Re: [PATCH] RFC: CODING_STYLE: describe "self" variable convention

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 11/20/19 1:54 PM, Marc-André Lureau wrote:
> Following the discussion in thread "[PATCH v3 13/33] serial: start
> making SerialMM a sysbus device", I'd like to recommend the usage of
> "self" variable to reference to the OOP-style method instance, as
> commonly done in various languages and in GObject world.
> 
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>   CODING_STYLE.rst | 38 ++++++++++++++++++++++++++++++++------
>   1 file changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/CODING_STYLE.rst b/CODING_STYLE.rst
> index 427699e0e4..cb6635af71 100644
> --- a/CODING_STYLE.rst
> +++ b/CODING_STYLE.rst
> @@ -102,12 +102,38 @@ Rationale:
>   Naming
>   ======
>   
> -Variables are lower_case_with_underscores; easy to type and read.  Structured
> -type names are in CamelCase; harder to type but standing out.  Enum type
> -names and function type names should also be in CamelCase.  Scalar type
> -names are lower_case_with_underscores_ending_with_a_t, like the POSIX
> -uint64_t and family.  Note that this last convention contradicts POSIX
> -and is therefore likely to be changed.
> +Variables are lower_case_with_underscores; easy to type and read.
> +
> +The most common naming for a variable is an abbreviation of the type
> +name.  Some common examples:
> +
> +.. code-block:: c
> +
> +    Object *obj;
> +    QVirtioSCSI *scsi;
> +    SerialMM *smm;
> +
> +When writing QOM/OOP-style function, a "self" variable allows to refer
> +without ambiguity to the instance of the method that is being
> +implemented (this is not very common in QEMU code base, but it is
> +often a good option to increase the readability and consistency,
> +making further refactoring easier as well).  Example:
> +
> +.. code-block:: c
> +
> +    serial_mm_flush(SerialMM *self);
> +
> +    serial_mm_instance_init(Object *o) {
> +        SerialMM *self = SERIAL_MM(o);
> +        ..
> +    }
> +
> +Structured type names are in CamelCase; harder to type but standing
> +out.  Enum type names and function type names should also be in
> +CamelCase.  Scalar type names are
> +lower_case_with_underscores_ending_with_a_t, like the POSIX uint64_t
> +and family.  Note that this last convention contradicts POSIX and is
> +therefore likely to be changed.
>   
>   When wrapping standard library functions, use the prefix ``qemu_`` to alert
>   readers that they are seeing a wrapped version; otherwise avoid this prefix.
> 

So in this example:

static void pci_unin_agp_init(Object *obj)
{
     UNINHostState *s = UNI_NORTH_AGP_HOST_BRIDGE(obj);
     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
     PCIHostState *h = PCI_HOST_BRIDGE(obj);

     /* Uninorth AGP bus */
     memory_region_init_io(&h->conf_mem, OBJECT(h),
                           &pci_host_conf_le_ops,
                           obj, "unin-agp-conf-idx", 0x1000);
     memory_region_init_io(&h->data_mem, OBJECT(h),
                           &pci_host_data_le_ops,
                           obj, "unin-agp-conf-data", 0x1000);

     object_property_add_link(obj, "pic", TYPE_OPENPIC,
                              (Object **) &s->pic,
                              qdev_prop_allow_set_link_before_realize,
                              0, NULL);

     sysbus_init_mmio(sbd, &h->conf_mem);
     sysbus_init_mmio(sbd, &h->data_mem);
}

You would change 'Object *obj' -> 'Object *self'?

But here we want to keep 'klass', right?

static void gpex_host_class_init(ObjectClass *klass, void *data)
{
     DeviceClass *dc = DEVICE_CLASS(klass);
     PCIHostBridgeClass *hc = PCI_HOST_BRIDGE_CLASS(klass);

     hc->root_bus_path = gpex_host_root_bus_path;
     dc->realize = gpex_host_realize;
     set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
     dc->fw_name = "pci";
}

Maybe we should restrict 'self' as name of Object type only?
But your example is with SerialMM, so no?