Re: Returning nil vs returning nothing
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- Subject: Re: Returning nil vs returning nothing
- From: Sean Conner <sean@...>
- Date: 2020年10月29日 17:42:59 -0400
It was thus said that the Great Grzegorz Krasoń once stated:
> Function that returns nothing seems different than function that returns
> `nil`:
>
> ```lua
> function f()
> return nil
> end
>
> function g()
> end
>
> print(f()) -- prints nil
> print(g()) -- prints empty line
> ```
>
> How to recognize this at the function call? For example how to implement an
> universal wrapper that would suppress all errors and still returns exactly
> the same thing as wrapped function in case of success?
I can't say I'm surprised that no one mentioned a C solution. It's
actually trivial in C:
#include <lua.h>
#include <lauxlib.h>
static int supress(lua_State *L)
{
lua_pcall(L,lua_gettop(L)-1,LUA_MULTRET,0);
return lua_gettop(L);
}
int luaopen_supress(lua_State *L)
{
lua_pushcfunction(L,supress);
return 1;
}
And the script:
supress = require "supress"
function f()
return nil
end
function g()
end
function h(...)
return ...
end
print(f()) -- prints nil
print(g()) -- prints empty line
print(h(1,2,3,4,5)) -- prints parameters
print(supress(f)) -- prints nil
print(supress(g)) -- prints empty line
print(supress(h,1,2,3,4,5)) -- prints parameters
prints the following:
nil
1 2 3 4 5
nil
1 2 3 4 5
I think the question I have is "why?" Why do you need such functionality?
And what would you do when pcall() (or lua_pcall()) fails?
-spc