[Python-Dev] Type hints -- a mediocre programmer's reaction (original) (raw)

Tue Apr 21 15:16:19 CEST 2015

Flow’s type checking is opt-in — you do not need to type check all 
your code at once. However, underlying the design of Flow is the 
assumption that most JavaScript code is implicitly statically typed; 
even though types may not appear anywhere in the code, they are in 
the developer’s mind as a way to reason about the correctness of the 
code. Flow infers those types automatically wherever possible, which 
means that it can find type errors without needing any changes to 
the code at all. On the other hand, some JavaScript code, especially 
frameworks, make heavy use of reflection that is often hard to 
reason about statically. For such inherently dynamic code, type 
checking would be too imprecise, so Flow provides a simple way to 
explicitly trust such code and move on. This design is validated by 
our huge JavaScript codebase at Facebook: Most of our code falls in 
the implicitly statically typed category, where developers can check 
their code for type errors without having to explicitly annotate 
that code with types.