classes prop needs to be memoized

Maybe I am interpreting this wrong, but I believe that if I pass a classes prop to a component wrapped with withStyles, that component always re-renders with the parent, even if no props change.

const myClasses = { test: 'myClass' };

class MyComponent extends React.PureComponent {
  render() {
    return (
      <MySecondComponent classes={myClasses} />
    );
  }
}

I believe what’s happening is when MySecondComponent is checked for updates, withStyles generates a new object despite the fact that its classes prop has not changed. https://github.com/mui-org/material-ui/blob/v1-beta/packages/material-ui/src/styles/withStyles.js#L234

This causes the SecondComponent to always re-render, despite its props not changing.

[oliviertassinari]

In the future, we could also try to memoize the classes when users are providing a classes property.

Yep: #8142

[CharlesStover]

PR open, sorry for the delay. I had trouble getting yarn build to work on my machine, so I just used babel-es2015 stage-0 react and replaced the node_module on my machine to test. Worked great. I think it only added ~600 bytes for an uncompressed transpile.