Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release)
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- Subject: Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release)
- From: David Manura <dm.lua@...>
- Date: Tue, 5 May 2009 21:47:42 -0400
On Tue, May 5, 2009 at 2:20 PM, Petite Abeille wrote:
> Well, Objective-C had the concept of "category" for the longest time,
> and it hasn't collapse on its own weight yet.
That [1] looks like fun ;) The run-time check
"OBJC_PRINT_REPLACED_METHODS" apparently offers some help though,
perhaps somewhat similar to the "name conflict for module" error in
Lua's module function (loadlib.c).
I think it would be ideal if we could inject only lexically (the
injection limited to the lexical scope). With discipline, the wrapper
allows something like that:
On Mon, May 4, 2009 at 3:32 AM, steve donovan wrote:
> function module_fun (s1, s2)
> s1,s2 = S(s1),S(s2)
> ...
> ... s:trim() etc
> end
but we must not carelessly pass the wrapped object to functions
outside of the lexical scope expecting a string. We cannot guarantee
that our wrapper behaves exactly like a string because Lua strings are
not fully virtualizable [2].
An alternate idea is to modify the string metatable to be scope aware:
-- framework
local mt = debug.getmetatable('')
local scope = {}
function mt.__index(s, k)
local f = debug.getinfo(2, 'f').func
return scope[f] and scope[f][k] or string[k]
end
local function scoped_string_methods(t)
local f = debug.getinfo(2, 'f').func
scope[f] = t
end
-- test example libraries
local stringx = {}
function stringx.trim(self) return self:match('^%s*(%S*)%s*$') end
local stringxx = {}
function stringxx.trim(self) return self:match('^%s?(.-)%s?$') end
-- test example
function test2(s)
assert(s.trim == nil)
scoped_string_methods(stringxx)
assert(s:trim() == ' 123 ')
end
function test(s)
scoped_string_methods(stringx)
assert(s:trim() == '123')
test2(s)
assert(s:trim() == '123')
end
local s = ' 123 '
assert(s.trim == nil)
test(s)
assert(s.trim == nil)
print 'DONE'
[1] http://kevincathey.com/code/detecting-conflicting-objective-c-category-methods/
[2] http://lua-users.org/wiki/LuaVirtualization
- References:
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), Luiz Henrique de Figueiredo
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), steve donovan
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), Henk Boom
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), Philippe Lhoste
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), David Manura
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), Henk Boom
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), Petite Abeille
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), steve donovan
- Re: Injecting names & method chaining (was Re: [ANN] Penlight Libraries, First release), Petite Abeille