Better API support for read only properties

[jreidinger]

Hi,
in newly added feature to support properties #86 there is missing better support for quite common read only properties.
Basically there are two main usage of read only properties that needs to send signal.

1. just given property is changed. Now it needs to use dbus_attr_reader, attr_writer and dbus_watcher for that single property.
2. bunch of read only properties are changed ( like read or refresh method ). It is now supported by dbus_attr_reader plus call PropertiesChanged which is good enough.

So if it would be possible to support better use case 1. something like dbus_ro_attr_accessor that combines that three calls.

[mvidner]

The simple idea is:

• read-write at the Ruby (implementation) side
• read-only at the D-Bus (API) side

[mvidner]

In case we change the API because of this, see also #115 where we may need to change the dbus_watcher API.

[mvidner]

Before:

dbus_attr_reader :foo, type
attr_writer      :foo
dbus_watcher     :foo

After, with the simple implementation change in #117:

attr_accessor :foo
dbus_reader   :foo, type  # must come second

@jreidinger what do you think?

[jreidinger]

For me new API looks reasonable. I expect similar it will looks for rw attr in dbus? so attr_accessor and then dbus_accessor?

[mvidner]

I expect similar it will looks for rw attr in dbus? so attr_accessor and then dbus_accessor?

Yes, and because it's a simpler case, it has a name: dbus_attr_accessor

A read-write property accessing an instance variable. A combination of attr_accessor and dbus_accessor.

[mvidner]

Solved in #117