Plugins: Methods for generated types

[abhinav]

Plugins should be able to generate methods for generated types. They will likely need access to information about the types themselves.

[hlin117]

It would be nice if there were nice ways to map thrift enums to thrift enum pointers.

For example, if I have

enum ActionType {
    ENUM_ONE  = 1
    ENUM_TWO = 2 
    ENUM_THREE = 3
}

It would be nice if thrift-rw created a method called

func (a ActionType) Ptr() *ActionType {
    // Implementation here
}

[abhinav]

@hlin117 We could do this natively instead of through a plugin.

The namespace of methods attached to an enum type is controlled completely by
us so there are no concerns about conflicts. I see the value of that method
since you can't take pointers to consts otherwise.

Can you create a separate issue for this? Further, if you feel motivated, we
would welcome a PR implementing that. It should be pretty straightforward.
Otherwise, we'll be able to get to it as priorities allow.