To interface or not to interface

[Walter Bright]

Jason House wrote:
> Walter Bright Wrote:
> 
>> Jason House wrote:
>>> 7. Compiler-assisted verification.
>> For interfaces, the compile time checking is limited to verifying that
>> functions with the right signature are supplied. Templates can go
>> considerably beyond that with the constraint checking.
> 
> constraints are more powerful, but they have downsides: • If a class is
> incorrectly defined, failure to use a type without a constraint check leads
> to errors in the code using it instead of the class definition. Usage isn't
> always guaranteed to be correct either, so the developer must spend extra
> time diagnosing the real error. • If a class is incorrectly, initial usage
> without a constraint may completely miss the error. Easy examples would be a
> typo propogated with copy/paste, or neglecting to use save. • If a class is
> incorrectly defined and usage uses a constraint, the developer will simply
> get an error that there is no matching call. • If a constraint is incorrectly
> defined and usage uses the constraint, the developer will simply get an error
> that there is no matching call.
> 
> None of these scenarios are particularly helpful for a developer
> creating/expanding a family of objects.


You can also make constraints that give custom error messages, so you can do 
better than the compiler's stab at it. How good they are is up to the designer 
of the type.