Re: A Lua implementation of boost::bind

[Peter Cawley <lua@...>]

The following examples do not work as I'd expect them to:

bbind (print,nil) () --> nothing ; should be nil?
bbind (print,nil,_1) (1) --> nothing; should be nil 1?
bbind (print,_3,_3) (1,2,3) --> table table; should be 3  3?

On Mon, Apr 6, 2009 at 2:51 PM, steve donovan <steve.j.donovan@gmail.com> wrote:
> Hi all,
>
> This demonstrates how to implement boost::bind while still producing
> an efficient binding. The key is code generation. So e.g. bbind
> (print,_2,_1,true) will generate the following code string:
>
> return function (fn,_v1)
>        return function(_1,_2) return fn(_2,_1,_v1) end
> end
>
> Which is then compiled and called twice, first to compile the wrapper
> function and next to extract the wrapped function.
>
> This is of course a relatively expensive function, but the resulting
> binding is fast.
>
> steve  d.
>
>
> -- testbind.lua
> -- Lua implementation of boost::bind
> -- http://www.boost.org/doc/libs/1_38_0/libs/bind/bind.html
> local append = table.insert
> local concat = table.concat
>
> _1,_2,_3,_4,_5 = {'_1'},{'_2'},{'_3'},{'_4'},{'_5'}
> local placeholders = {[_1]=true,[_2]=true,[_3]=true,[_4]=true,[_5]=true}
>
> function bbind(fn,...)
>        local args = {...}
>        local holders,parms,bvalues,values = {},{},{'fn'},{}
>        local np,nv = 1,1
>        for i,a in ipairs(args) do
>                if placeholders[a] then
>                        append(holders,a[1])
>                        append(parms,'_'..np)
>                        np = np + 1
>                else
>                        local v = '_v'..nv
>                        append(bvalues,v)
>                        append(holders,v)
>                        append(values,a)
>                        nv = nv + 1
>                end
>        end
>        bvalues = concat(bvalues,',')
>        parms = concat(parms,',')
>        holders = concat(holders,',')
>        local fstr = ([[
> return function (%s)
>        return function(%s) return fn(%s) end
> end
> ]]):format(bvalues,parms,holders)
>        local res,err = loadstring(fstr)
>        res = res()
>        return res(fn,unpack(values))
> end
>
>
>
> bbind (print,_1,_2,true) (1,2)
> -- 1    2       true
> bbind (print,_2,_1,false) (1,2)
> -- 2    1       false
> bbind (print,_2,_1) (1,2)
> -- 2    1
> bbind (print,10,_1,20) (1)
> -- 10   1       20
>