Add read only version property

[snuyanzin]

Sometimes it is more convenient to have !version command than to restart sqlline to see startup message with version and then to reinitialize connections.

[julianhyde]

Are you saying that the !version command would re-initialize connections?

Another way to accomplish this is to use the command that displays properties, namely !set with no arguments. version is a read-only property, whereas outputformat is a read-write property.

What are the pros and cons of that approach? Are there any other read-only properties that we might be interested in?

[snuyanzin]

Are you saying that the !version command would re-initialize connections?

No. The only thing it does is printing current version.

About reinitialization I mean that now the only way to know version is restart which leads to reinitialization.

Are there any other read-only properties that we might be interested in?

I could imagine a list of plugged in command handler classes and application class.

What are the pros and cons of that approach?

Well the only cons of properties usage I see is !set provides the output of all existing properties.
However after merging of #143 the problem should gone.

[julianhyde]

OK, so it would seem that !set version would be a viable alternative after #143.

What do you think we should do? I am happy with either approach. I just hope we're not on a slippery slope to other commands (say !jdkVersion or !locale or !timezone) in future.

[risdenk]

Going to ask the question - does version need to be exposed in an interactive manner?

Assuming sqlline is command line invoked, can't a second shell (ssh, tmux, screen, etc) be opened to check the version of sqlline? If sqlline was upgraded behind the scenes after opening sqlline that would be a weird scenario.

I'm not sure of other command line tools that expose the version after you are already inside them after the initialization. Some don't even print it during the initialization.

[julianhyde]

SQLPlus does what I am suggesting: https://stackoverflow.com/questions/9021581/how-to-know-sqlplus-version-from-inside-sqlplus

[risdenk]

Ah thats a nice example. Thanks

[snuyanzin]

What do you think we should do? I am happy with either approach. I just hope we're not on a slippery slope to other commands (say !jdkVersion or !locale or !timezone) in future.

Agree. It is not good to make such precedents. I do not have strict requirements to have it as !version rather than !set version.
Thank you for the discussion.
I will update the PR with implementation it as !set version and will rename the issue

[julianhyde]

Fixed in c222391; thanks @snuyanzin!