Lua calls to booleans defined different ways

[ExpiredReign]

I'm trying to understand how booleans are parsed (I think that is the term) by Lua when they are defined a number of different ways.

eg.
In CIV5Buildings.xml the defining of a number of tables are laid out and most of the booleans are done like:

<Column name="ArtInfoRandomVariation" type="boolean" default="false"/>

but some are defined as:

<Column name="RequiresUniquePlayers" type="bool"/>

Now when you examine these tables with SQLiteSpy all the booleans defined in the first manner are 0 or false, unless later modified to be 1 or true. Whereas the booleans defined in the second manner are empty or null, unless changed to 1 or true.

What I want to know is, if you have Lua code that makes a check of a boolean, expecting it to be 0 or false, and it finds it as null, as the second table example shows it, won't that produce an error?

Secondly, I have found that the Notifications table, as examined with SQLiteSpy, shows the booleans defined there as "false" or "1". If someone wrote Lua code that asked if a value was false this way:

if someValue < 1 then...

(don't pick on the poor code)
Would it fail because the value was stored as "false"? Or are these values recognized as booleans no matter which manner they are stored?

 

[whoward69]

In Lua, when evaluated as a condition, only false and nil are false, everything else is true (unlike some other languages where 0 and/or the empty string are also considered as false) - see http://lua-users.org/wiki/ExpressionsTutorial

Sqllite has no boolean datatype (all booleans are stored as ints - either 0 or 1) - see http://www.sqlite.org/datatype3.html

The Civ5 game core DLL does the conversion for you, so if you access GameInfo.Table[index].BooleanColumn it will give you a Lua boolean value (and not an int). The only time you need to know/care what's in the database is if you directly access the column value via DB.Query()

Bottom line, if the XML files say its a boolean and you don't use direct database lookups, treat it as a boolean in Lua.

 

[ExpiredReign]

Excellent. I knew you would have the answer.

I think I read you teach at a university? I hope the students there appreciate your insight as much as I do. Thank you very much.

 

[whoward69]

I think I read you teach at a university?

Not me, although I have worked for several universities and given training courses in various IT subjects, but I have been writing code for more years than I care to remember (any other ex-Fortran4 coders here?)

 

[ExpiredReign]

Well that doesn't matter, you are here helping plenty of us understand the coding process. For that I thank you.