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Date: Fri, 07 Oct 2011 12:20:39 +0100
From: RedGrittyBrick <RedGrittyBrick@spamweary.invalid>
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Subject: Re: in praise of [loosey goosey] type checking)
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On 07/10/2011 11:50, RedGrittyBrick wrote:
> On 06/10/2011 07:33, Roedy Green wrote:
>> I changed the result of a widely used method from boolean to int. The
>> neat thing was the compiler (actually the Intellij syntax checker)
>> made sure I fixed up every invocation of that method. It would not let
>> me forget even one.
>>
>> Imagine a language with loosey goosey type checking where it was
>> entirely up to you entirely to ensure all the invocations were
>> corrected. You could never be sure.
>
> The problem might not arise. Depending on which language you mean and
> how you apply your knowledge of the language to the intended use of the
> method.
>
> For example, in Perl, if I changed a method so that it returned an
> integer instead of a boolean I would do so in such a way that any
> existing code calling that method could continue to function unchanged.
> Perl can quite happily treat any integer as a boolean, I would just have
> to ensure that I return an integer value that will be treated as (say)
> false under circumstances where the original method would have been
> expected to return false.

To illustrate:

Let's say I have an object "store" and I have a method "contains()" that 
takes an argument and returns boolean telling us if the store contains a 
matching element. I might use it thusly in a zillion places

     if ($store.contains($APPLE)) {
       $store.sell($APPLE);
     } else {
       die "Out of $APPLE!";
     }

Now lets say I change contains() to return a count instead of a boolean.

My zillions of places treating the return value as boolean still work 
unchanged. Hurrah for loosey goosey!

-- 
RGB