Feature request: Make "in" blocks part of the public interface

[monarch_dodra]

This is mostly related to the discussion that took place on page 
2 of this thread:

http://forum.dlang.org/thread/ezjiwnydlhtwqoemrmxn@forum.dlang.org?page=2

The issue (as I see it), is that the "contract blocks" in/out, 
are meant to verify the data that is passed to and from the 
function, rather than verify the implementation of said function.

The problem is that it's "conditional execution" is tied to the 
release mode of the compiled function, as opposed to the release 
mode of the caller's code.

This means that if you are using somebody else's lib, his code 
will gladly accept your erroneous data, and crash, with no 
warning to you.

An obvious example would be the (theoretical) sqrt methods, that 
could restrict via "in" that the input is positive: Once they are 
written and fully verified, they are compiled and released in 
release mode. But that doen't mean somebody using it in his new 
code won't accidently call it with a negative number... and sqrt 
will fail to see it.

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I'd like to request (but I don't know how feasable this is), that 
"in/out" blocks be made part of the public interface of a 
function, and that it be compiled by the *caller* code (according 
to his flags), and *not* the function itself.