Re: __tostring and string.format

[steve donovan <steve.j.donovan@...>]

On Mon, Dec 6, 2010 at 6:45 AM, HyperHacker <hyperhacker@gmail.com> wrote:
> Why does string.format not call tostring() on arguments given as %s?
> (and for that matter tonumber() for %d/%u, which in turn could call a
> __tonumber metamethod...)

This bit me recently and I'm now using a more paranoid version:

local format = string.format

function formatx (fmt,...)
    local args = {...}
    local i = 1
    for p in fmt:gmatch('%%s') do
        if type(args[i]) ~= 'string' then
            args[i] = tostring(args[i])
        end
        i = i + 1
    end
    return format(fmt,unpack(args))
end

print(formatx('%s=%s',10,nil))

string.format is one of the important string functions and it would be
good if this kind of behaviour was built-in and hence more efficient.

But then we could ask the very same question about table.concat, which
also doesn't use tostring...

steve d.