Re: Better Syntax?

[云风 Cloud Wu <cloudwu@...>]

Mike Jones <mike@mikejones.in>于2016年10月3日周一 下午6:44写道：

Hi,

I am working on a project where I have basically an event style
framework, and I would like some way to "chain together" functions. I
have had a quick look at OO libraries for Lua but they don't seem to
be suited to what I am trying to do. I can't seem to find an example
that fits my use case of wanting parrallel modules providing the same
functions.

Here is a short example of what I am doing at the moment:

-- core function, defined in common header
function dosomething(arg)
    print("Orginal dosomething()")
   return 0
end

-- module 1 included in script, adds extra code on to existing function
pre_module1_dosomething = dosomething
function dosomething(arg)
    print("Module 1 dosomething()")
    return pre_module1_dosomething(arg)
end

In my example the functions are in different files, but that's the
basic pattern I am currently using to chain extra code on to the end
of a function that has already been defined. When executed it should
output "Module 1 dosomething()" followed by "Original dosomething()",
ie both functions get executed. Is there a better way of achieving
this sort of functionality? the use of the "pre_module1_dosomething"
variable to hold the parent function seems very ugly to me.

- Mike Jones

How about this one ?

function dosomething(arg)

  print("Orginal dosomething()")

  return 0

end

local hook = {}

function hook.dosomething()

print("Module 1 dosomething()")

end

local function inject(original, hook)

for method, func in pairs(hook) do

local pre = original[method]

original[method] = function (...)

func(...)

return pre(...)

end

end

end

inject(_ENV, hook)

print(dosomething())