Re: Nil and false in Lua design

[Thomas Jericke <tjericke@...>]

On 10/14/2013 07:16 PM, Sean Conner wrote:
>   
> 	if info.use_extention_a ~= nil and info.use_extension_a then
> 	  ...
> 	end
>
> 	if info.use_option_2 ~= nil and info.use_option_2 then
> 	  ...
> 	end
>
>    In other words---it becomes a royal pain in the butt.  And for what?  A
> bit of purity? [2]
Actually you are simply testing for the value "true" here.

	if info.use_extention_a == true then
	  ...
	end

	if info.use_option_2 == true then
	  ...
	end

Looks a little strange, because comparing to 'true' is usualy not 
necesesarry. But info.use_extention_a could be non boolean so it 
actually makes sense. This assumes that equality between different types 
is still allowed and returns false if types are different.

There are less theoretical situations where the current implementation 
is unintuitive. Mostly the 'or' and 'and' operators. They do not only 
accept non boolean values, they also return non-boolean values. typeof(A 
or B) could be anything, and 'A' and 'B' don't even have to change their 
types for "A or B" to change its type.

typeof(true or 10) -- boolean
typeof(false or 10) -- number

--
Thomas