Take some of the magic out of traits by insisting traits be instances, not classes

[jasongrout]

As Sylvain proposed in #48,

class Foo(HasTraits):
    bar = Int    # deprecated
    baz = Int()  # ok
    alpha = List(trait=Int)     # deprecated
    alpha = List(trait=Int())   # ok

[jasongrout]

This will require quite a few changes to other repos, because things like List(Unicode, ...) are used a lot throughout IPython.

[jasongrout]

This line, changing warnings to errors, should be removed for the final version of this PR. This just makes it really easy to see where things break.

[SylvainCorlay]

Jason reviews his own pull requests :)

I am 👍 on this change. This deprecates half of the code of the metaclass.

[jasongrout]

Hey, I write them with my right brain, I review them with my left!

[jasongrout]

Yes, I think the deprecation should happen in 4.1, removal in 5.0

[minrk]

Sounds good.

[ellisonbg]

I am +1 on this change.

On Thu, Jul 16, 2015 at 3:11 PM, Min RK notifications@github.com wrote:

Sounds good.

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Brian E. Granger
Cal Poly State University, San Luis Obispo
@ellisonbg on Twitter and GitHub
bgranger@calpoly.edu and ellisonbg@gmail.com

[jasongrout]

I think this (and the related commits in different repos noted above) are ready for review now.

[jasongrout]

ping on merging this. Because both this and the metadata PR change the same lines when upgrading our code, I'd like to base the metadata pr on this one, and that's easier if this is merged into master.

[SylvainCorlay]

cool!