What are the approaches to typing conditionals and their tradeoffs?

1st approach: True and False branches must be of the same types.

Pros:

• Simple to implement and understand.

• The precise type of the conditionals is mostly unambiguous.

  Cons:

• Inflexible: Dynamic dispatches are harder to express, for example.

• Not expressive.

2nd approach: The type of the conditionals is the Union type of both branches.

Pros:

• More flexible: Each branch can return an arbitrary type.

  Cons:

• The consumer of the results of conditionals must use some techniques like If-splitting.

3rd approach: The type of the conditionals is the least upper bound of both branches.

Pros:

• Flexible.

  Cons:

• The exact typing of each branch is lost.