[Issue 20428] Precondition bug for in/out

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20428

Dennis <dkorpel at live.nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |contracts
                 CC|                            |dkorpel at live.nl
           Hardware|x86_64                      |All
                 OS|Linux                       |All
           Severity|critical                    |enhancement

--- Comment #3 from Dennis <dkorpel at live.nl> ---
Not a bug, derived classes must tighten the outputs but can loosen the inputs:
https://dlang.org/spec/function.html#in_out_inheritance

Running checks on derived classes would break valid code.

Changing this to an enhancement "copy parent's contracts by default" like 
FeepingCreature suggested, though that might need a DIP since it's a breaking
change as well.

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