Add the feature for go-lang like Defer

[kylincaster]

The Defer function refers to take some operation on the exit of the section or the function, which is very convinient for case with resouce need to be released afterwards.
For example in the function with the multiple exit like.

function connect(...)
f = open(file)

if condition
	close(f)
	return ...
else
	close(f)
	return xxx

if the defer feature is added, the code could be simplied as

function connect(...)
f = open(file)
@defer close(f)
if condition
	return ...
else
	return xxx

I suggest to implement @defer as

macro defer(f(x...))
	ccall(:jt_func_defer, f, x...)
end

where :jt_func_defer is some julia C-interface which invokes the expression f(x...) at the exit of function.

[gbaraldi]

I believe there is https://github.com/adambrewster/Defer.jl which kinda does this.

[kylincaster]

I believe there is https://github.com/adambrewster/Defer.jl which kinda does this.

Thank you I have a try on Defer, which works exactly as I expected.

[KristofferC]

See also the long discussion in #7721.