Re: Validate parameters to Lua functions

[Jerome Vuarand <jerome.vuarand@...>]

2011/4/8 C++ RTMP Server <crtmpserver@gmail.com>:
>
> On Apr 8, 2011, at 12:11 PM, Sean Conner wrote:
>
>> It was thus said that the Great C++ RTMP Server once stated:
>>> Hello all,
>>>
>>> I'm just trying the depth of the ocean with my finger here...
>>>
>>> Is it somehow possible to validate the number/types of parameters for lua
>>> functions from C/C++? More details ...
>>>
>>>
>>> I already embedded lua as scripting engine in my project. What I do is to
>>> load the lua script, inspect the existence of certain lua functions in the
>>> script and if they exists I will call them when the time comes. Now, is it
>>> possible to also introspect/reflect on the number/types of parameters?
>>>
>>> Some pseudo code:
>>>
>>> if unable to load lua script
>>>      return false
>>>
>>> foreach functionName in functionsNamesList do
>>>      if functionName doesn't exist //this works just fine
>>>              continue
>>
>>  Yes, this you can do.
>>
>>>      if functionName parameters count different from expected //maybe possible
>>>              continue
>>
>>  Nope.  All you can really do is see if the function exists.  It's up to
>> the function itself to check the paramters it gets.
> My scenario is the other way around. I let the user define a lua callback function. I know the if he defines myHandlerForMyCustomEvent function, I should call it from the C++ when MyCustomEvent is triggered. Now, before calling it from C/C++, what I would like is to see if, at least, has the proper number of arguments (if determining the type is not possible). Otherwise, the user is bound to make mistakes. If C/C++ expects myHandlerForMyCustomEvent function to have 3 params and the user defines that function with only 1 parameter, I would like to warn him/her before continuing:
>
> "Hey, myHandlerForMyCustomEvent function is not defined properly for C/C++ needs! It will definitely not do the job because you missed 2 params"

IIRC you can do that with the debug API, but it's not a common idiom.
If the user doesn't care about the extra parameters, why force him to
declare them?