Re: file:write() fails silently for read-only files

[Dirk Laurie <dpl@...>]

On Tue, Sep 06, 2011 at 08:39:00AM +0200, HyperHacker wrote:
> Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
> > f=io.open('foo.foo', 'r')
> > f:write('ffd')
> > f:close()
> >
> 
> Call me crazy, but I feel like f:write() should throw an error when
> trying to write to a read-only file, instead of just doing nothing.

There are two ways of handling errors: testable return values, and
throwing errors.  Among programming languages that I use, Lua is unique
in giving you a seamless way of overriding whatever default choice it
has made.  So you can do this:

local io_write = io.write
io.write = function(...)
    local test, message, code = io_write(...)
    if test==nil then error(message,2) end
    end

If io.write had thrown an error instead, you could similarly have
overridden it by a wrapper that uses pcall.

Dirk