prefer capturing `this` as `self`.

I'm not a big fan of `_this`. To me, `_` typically denotes something private with respect to the externally visible API. That has no bearing on the capturing of context and therefore its a weak convention. I'd prefer to use `self`. 
`self` is OK to me but even better is naming the variable with what it is like if it was used externally. I guess it doesn't apply here though since it is context less.