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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada and "early return" - opinion/practice question
Date: Mon, 15 Mar 2021 18:02:09 +0100
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On 2021-03-15 17:46, John McCabe wrote:
> I hope this isn't a FAQ (it's hard to find relevant articles) but can someone guide me on the 'normal' treatment in Ada style of what appears to be referred to (by C/C++ programmers) as early-return.
> 
> For example, you have a C++ function (pseudo code sort of thing):
> 
> <sometype> fn(<some parameters>)
> {
>      if (<some undesirable condition 1>)
>      {
>          return <something bad happened 1>;
>      }
> 
>      if (<some undesirable condition 2>)
>      {
>          return <something bad 2>;
>      }
> 
>      if (<some undesirable condition 3>)
>      {
>          return <something bad 3>;
>      }
> 
>      // Only get here if everything's good...
>      <do some real stuff>
>      return <something good>;
> }
> 
> I've probably mentioned this before, but it's a long time since I used Ada in anger and I don't remember seeing stuff like that when I did use Ada a lot; does anyone write stuff like that in Ada?

> When I first learnt to program properly it was using Pascal with, as I remember it, only one return from a function being allowed, so over the years I've mostly looked at positive conditions and indented stuff, pulling the stuff in the middle out into its own procedure or function where appropriate, but you see so many people defending this style in C/C++ that I wonder whether it really is defensible?

I see nothing wrong with it. In Ada:

    function fn (<some parameters>) return <sometype> is
    begin
       if <some undesirable condition 1> then
          return <something bad happened 1>;
       elsif <some undesirable condition 2> then
          return <something bad 2>;
       elsif <some undesirable condition 3> then
          return <something bad 3>;
       else --Only get here if everything's good...
          <do some real stuff>
         return <something good>;
    end fn;

P.S. The old mantra of structured programming was one entry, one exit. 
This is why some argued for single return while storing result code in a 
variable. Clearly adding a result variable would reduce readability 
rather than improve it.

P.P.S. One could debate exception vs. return code, but this is another 
story for another day.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de