`in` no longer same as `const ref`

[Olivier FAURE via Digitalmars-d]

On Monday, 30 January 2017 at 13:57:10 UTC, Adam D. Ruppe wrote:
> On Monday, 30 January 2017 at 00:26:27 UTC, Walter Bright wrote:
>> I was afraid that by checking it, too much code would break.
>
> Code that was using it improperly was *already* broken. Now, 
> the compiler will simply tell them, at compile time, why 
> instead of letting it silently accept undefined behavior.

Well, it's a trade-off. Some people would rather their project 
with potentially broken code does not stop compiling because they 
upgraded their compiler.

Although I guess you could solve this by having -dip1000 emit 
only warnings and no error until the adaptation period had passed.