Re: Liberty-eiffel Digest, Vol 57, Issue 1

[Hans Zwakenberg]

What would happen if neither of the two arguments in your example is void?  
Which of the two would be printed?



> liberty-eiffel-request@gnu.org hat am 30.06.2022 18:02 CEST geschrieben:
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> Today's Topics:
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>    1. default or foo (Paolo Redælli)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Thu, 30 Jun 2022 08:14:08 +0200
> From: Paolo Redælli <paolo.redaelli@gmail.com>
> To: liberty-eiffel mailing list <liberty-eiffel@gnu.org>
> Subject: default or foo
> Message-ID: <c5e17938-d64f-de8e-b1c7-eceae2ea0ce0@gmail.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
> 
> I propose to add a feature to ANY.
> 
> infix "or" (another: like Current): like Current
> 
>      do
> 
>          if another=Void then
> 
>              Result:=Current
> 
>          else
> 
>              Result:=another
> 
>          end
> 
>      ensure Result/=Void
> 
>      end
> 
> 
> to allow writing things like
> 
>      print("a default answer" or something_that_can_be_void)
> 
> instead of
> 
>      local temp: STRING
> 
>      do
> 
>          temp := something_that_can_be_void
> 
>          if temp=Void then
> 
>              print("a default answer")
> 
>          else
> 
>              print(temp)
> 
>          end
> 
>      end
> 
> 
> Inspired by the coalescing operators. See 
> https://en.wikipedia.org/wiki/Null_coalescing_operator
> 
> Initially I thought of proposing to allow to write "foo or default" like 
> in many other languages but this would require to add to the language a 
> special case to avoid an exception for a Void call.
> 
> Using a pattern "default or foo" just avoid this.
> 
> I think it will help writing expressive yet concise code. Think of it as 
> an Eiffel-style coalescing operator.
> 
> An altertive naming would be to use a free operator but I couldn't find 
> one that I like.
> 
> 
> 
> 
> 
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> End of Liberty-eiffel Digest, Vol 57, Issue 1
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