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Changing Lua function metatable

Started by tcsavage Jun 25, 2010 at 12:06 PM 4 replies 3.1k views

Original Post

Jun 25, 2010 at 12:06 PM

I have found myself wanting to override a function's __index and __newindex metamethods. The reason for this is I have a simple C function to expose data to Lua and set a global name (or table index) for it. This means that I can print a C variable myvar in Lua using print(myvar) and set it using myvar(value). I would like to re-wire __index and __newindex to make this more like print(myvar) and myvar=value.

Is this even possible? I have tried using the C API and the debug library without success.

dmail

Jun 25, 2010 at 2:45 PM

Functions in Lua do not have a metatable which you can alter on a per instance basis, so what you are trying to achieve with metamethods is not possible.
What is "myvar"? Table, function, other value type?

tcsavage

Author

tcsavage

Jun 25, 2010 at 2:55 PM

OK, i'll have to find another way to do this.

myvar in this instance is a function created using lua_pushcclosure.

dmail

Jun 25, 2010 at 3:02 PM

Quote:
Original post by tcsavage
OK, i'll have to find another way to do this.

To be honest I am not clear what it is you want to do.

Quote:

myvar in this instance is a function created using lua_pushcclosure.

So in the following what is it that you are trying to do

myvar=value

Are you trying to use syntactic sugar via the assignment operator to supply an argument to the function?

tcsavage

Author

tcsavage

Jun 25, 2010 at 3:43 PM

Yeah. Essentially I have pushed functions from the C API to access data in C land. A call to myvar() will return the data, myvar(5) will set the data to equal 5.

My aim (as you suspected) was to essentially map myvar() to act like a value rather than a function.

m_switch

Jun 25, 2010 at 5:03 PM

See:

ObjectProperties

Do note that these techniques have varying degrees of performance implications.

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