Re: [LuaJIT ffi] Misleading error message?

[Thomas Lauer <thomas.lauer@...>]

Mike Pall <mikelu-1107@mike.de> wrote:
> Thomas Lauer wrote:
> > The following code, run under Windows, produces an error message for
> > line 4 which IMHO is misleading at best but more probably spurious?
> > 
> > ffi=require('ffi')
> > ffi.cdef('void DebugBreak(void);')  -- Any function will do
> > if ffi.C.DebugBreak then print(ffi.C.DebugBreak) end  -- OK
> > if ffi.C.DebugBreak~=nil then print(ffi.C.DebugBreak) end
> > 
> > luajit.exe: f:\testffi.lua:4: attempt to compare 'void ()' with 'void *'
> 
> Well, the error message is correct. You're comparing a function
> with nil (which is treated like a pointer to void here).

Technically you're right. Any competent C programmer will have an idea
what this messages means and where it comes from. However, I assume that
the ffi functions will be used also by people who've not done a lot of C
programming.

> [But note that neither of two conditionals in your code can ever
> be true. Only nil and false are treated as not-true conditions.

I am not sure that I follow. Here, ffi.C.DebugBreak evaluates as true.

The actual code that triggered this mail is somewhat more involved than
the simplified example I gave.

-- 
cheers  thomasl