Re: Argument checking in Lua?

[Rici Lake <lua@...>]

On 1-Feb-06, at 2:48 PM, Chris Marrin wrote:

> Lua 5.1 has some nice argument checking functions, accessible from C, 
> like luaL_checknumber() and luaL_optstring(). But these are not 
> accessible from Lua, and I have not found anything roughly equivalent. 
> It would be easy to write such things, of course, by doing type(), 
> checking against nil and throwing errors. But is there any "standard" 
> way to do this? I have not been able to find anything...

I usually write:

  a = assert(tonumber(a), "number expected")

or, in the case where there is a sensible default:

  a = assert(tonumber(a or sensible_default), "number expected")

This doesn't produce error messages as nice as luaL_*, though.

Also, it doesn't work with strings, since tostring(x) pretty well 
always produces a string, in constrast with lua_tostring() which only 
coerces numbers. It would sometimes be nice to have a Lua function 
which acted like lua_tostring() and a C function which acted like 
tostring(). Of course, it's easy enough to write both of those.