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

FeepingCreature <default_357-line@yahoo.de> changed:

           What    |Removed                     |Added
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                 CC|                            |default_357-line@yahoo.de

--- Comment #1 from FeepingCreature <default_357-line@yahoo.de> ---
Sorta a bug but not really. More a really confusing aspect of how in-conditions work.

By substitutability, a subclass can always say that it chooses to accept more data as parameters than its parent class or interface demands. Contracts are an extension of this mechanism, so an in-condition on an interface is mostly useless - the subclass only *has to* accept all the values that the interface in-condition lets through; but it can always choose to accept more values. (This is fundamental to what inheritance formally means.)

In D, a lack of in-condition is taken to mean "the function takes any value allowed by the type." As such, you can always override a method with an in-condition with one that doesn't have an in-condition, which is taken to dissolve the in-condition.

Now, from a language design perspective it would probably be better if "no in-condition" meant "copy the in-condition of the parent interface" and you'd signal the desire to accept any value with something like "in (true)". However, that'd be a feature proposal, not a bug.

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

--- Comment #2 from FeepingCreature <default_357-line@yahoo.de> ---
Just to make it clearer:

interface I {
  void foo(int i) in (i < 10);
}

This means that for any implementation of I, foo() *has to* take all i < 10.

But it can always *choose* to additionally take i >= 10.

And by default, if you specify no in-condition in C : I {}, it does.

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

Dennis <dkorpel@live.nl> changed:

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

--- Comment #3 from Dennis <dkorpel@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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https://issues.dlang.org/show_bug.cgi?id=20428

Walter Bright <bugzilla@digitalmars.com> changed:

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           See Also|                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=23535

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

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
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           Priority|P1                          |P4

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

--- Comment #4 from dlangBugzillaToGithub <robert.schadek@posteo.de> ---
THIS ISSUE HAS BEEN MOVED TO GITHUB

https://github.com/dlang/dmd/issues/19645

DO NOT COMMENT HERE ANYMORE, NOBODY WILL SEE IT, THIS ISSUE HAS BEEN MOVED TO GITHUB

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