What's the best way to minimize the need of run time checks?

[BartC]

On 29/08/2016 03:43, Steve D'Aprano wrote:


> Your question seems to be, what happens if you follow that with an
> assignment to a different type?
>
> x = 5
> some_code(x)
> x = "hello world"
>
>
> Will the type-checker consider that an error ("you're assigning a str to an
> int") or will it infer that x is the Union[int, str]?
>
> Surely that depends on the type-checker! I don't think there's any hard and
> fast rule about that, but as far as I know, all statically typed languages
> consider than an error.

In C, you can write this:

  int x;

  x = 5;
  x = "hello";

With certain compilers (eg. gcc) you only get a warning. (And since I 
don't show warnings to avoid inundation, that seems to compile fine for me!)

But you write:

  x = 5.1;

with no errors or warnings.

>> A dynamic type inference
>> system could easily cope with this:
>>
>> x = 5
>> y = x**2
>> x = "five"
>> z = x.upper()
>>
>> and correctly deduce that, at the time of y's assignment,
>> exponentiation of x was legal, and at the time of z's, uppercasing
>> was.
>
> Could it? Do you have an example of a language or type-checker that can do
> that? This isn't a rhetorical question.

Actually the above example is one of the easiest to perform 
type-inference on, where the variable has been assigned a known type on 
the previous line!

-- 
Bartc