Type checking for Measurables

[rachel-fenichel]

Right now Measurables are checked with a combination of string equality tests against the type property and calls to isCorner(), isInput(), etc.

We need to pick a standard approach and use it everywhere.

From discussion with @samelhusseini :

I would prefer that as well. I wanted to leave the types as is round corner instead of adding the left, as there's a few places that check the type directly rather than using the base method isRoundCorner.

In terms of dealing with types, here are a few options:

• do what we're doing now, con with that is that the check method is on the measurable, ie: to add additional types you have to do them in base measurable, otherwise elem.isSpecialType() might not exist on all elements.
• factory type checker, something like: Blockly.isSpecialType(elem) that gets passed in an element and checks the type. This can be extended independently in each renderer to types that only matter there.
• Use a enum flag and bitwise operations with types. This is the option I prefer, but it might be an overkill. We could have a central place to register types, which basically internally appends new types to a enum flag. Then you can do things like:
  if (elem.type & Blockly.Measurable.Types['left row']) {
  }
  The nice thing about enum flags is you can have union types, so you can do bitwise checks to find if an element is a corner (not really caring about the specific type of corner it is), but then again you could always just do indexOf('corner') haha.

A combination of 2 and 3 would be nice too.

[samelhusseini]

Fixed.