show(o::Any) handles circular references

[amitmurthy]

This small patch specifically only handles the looping associated with self-referential compound types which do not have a show method.

It is a temporary fix till the larger issues of a better show is available. Works by recording already printed objects in a task local Set.

Will be useful for new user defined types with self-referential objects that do not have a show method.

[jiahao]

bump

Is this still relevant for 0.2-rc1?

[StefanKarpinski]

Now that we're past 0.2, it would be good to revisit this.

[quinnj]

Bump. This would be good to have for 0.3 (and this PR has been open a long time...)

[JeffBezanson]

Ok, let's rebase this, kick the tires, and see if we like it.

[quinnj]

Ok, I'm playing around with this. The original from this PR is:

In  [2]: type A
    b
end

In  [3]: type B
       a::A
       function B()
         self = new()
         self.a = A(self)
         self
       end
end

In  [4]: b = B()

Out [4]: B(A(B(# oid 2006584968323742060)))

I don't think showing the object id tells you much, how about something like:

In  [14]: show2(B())
B(A(B(#= circular reference =#)))

[porterjamesj]

Python uses ...:

Python 2.7.6 (default, Nov 15 2013, 15:57:34)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.2.79)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a = []
>>> a.append(a)
>>> a
[[...]]
>>>

[jiahao]

Whereas we could use ⥀ or the like.

[amitmurthy]

Rebased. Uses all 3 of ⥀, ... and the last 6 hex digits of the object id, like this - B(A(B(⥀ ...0ca5ab))) .

But I am neutral to any representation. Just thought that the object id may help in multiple circular references.

[quinnj]

I still vote for

In  [14]: show2(B())
B(A(B(#= circular reference =#)))

Very clear that something different is happening (in the case you accidently create a circular reference). And it uses a #= =# comment, and those are just nifty :)

[amitmurthy]

Have changed it to #= circular reference =# . Will go ahead and merge after a day or two if there are no objections.

[quinnj]

+1