Re: [ANN] Lua 5.2.0 (beta-rc5) now available

[Lorenzo Donati <lorenzodonatibz@...>]

On 04/07/2011 22.19, David Manura wrote:
> On Mon, Jul 4, 2011 at 3:40 PM, Luiz Henrique de Figueiredo
> <lhf@tecgraf.puc-rio.br>  wrote:
> > Lua 5.2.0 (beta-rc5) is now available [...]
> >         - clarifications between 'deprecated' and 'removed'
>
> This way of removing functions might not be ideal:

I totally agree.

[...]

> The reason is that to test whether a function exists, it is not as simple as
>
>    if io.popen then ..... end
>
> Rather, you need to wrap it in a pcall, and in the case of popen you
> need to pass some suitable argument that probably will always work
> (e.g. "echo").
>
> Alternately, you could test versions (e.g. _VERSION).
[...]

I understand that Lua team maybe intended to warn the user that his 
version of Lua doesn't support io.popen on his platform, but this seems 
too much hand-holding to me.

Maybe a stronger emphasis in the manual on checking the existence of 
popen before using it could be added instead.

For example (emphasis on new text):


"This function is *highly* system dependent and is not available on all 
platforms. *If you are not sure whether your system supports popen, 
check its existence explicitly in advance.*"

And if more hand-holding is deemed useful, add a snippet:

if io.popen then
 -- do something
end


> The recent discussion about whether string.foo should raise an error
> [2] is related to this.
>
> [1] http://www.sitepoint.com/why-browser-sniffing-stinks/
> [2] http://lua-users.org/lists/lua-l/2011-06/msg01382.html

-- Lorenzo