Hidden argument kind antipattern

[spir]

On 04/20/2011 01:09 AM, Vladimir Panteleev wrote:
> To elaborate, I mean allowing code which appears to behave surprisingly
> different from the at-a-glance interpretation, unless the programmer knows the
> function's signature. I've noticed a worrying adoption in D of this
> "antipattern", which, frankly, I believe doesn't belong in a well-designed
> programming language. One classic example of this is passing arguments by
> reference, something D inherited from C++. For example:
>
> int x, y;
> // ...
> someObject.updateCoords(x, y);
>
> What can you say about this code? The unobvious and surprising interpretation
> of it is that updateCoords will change the values of x and y. C# solved this
> problem neatly by requiring to specify the "ref" keyword before the function
> arguments:
>
> someObject.updateCoords(ref x, ref y); // much clearer
>
> This problem carries over to lazy parameters, as well. I'll quote a line of
> code from a recent post by David Simcha:
>
>> auto connections = taskPool.workerLocalStorage(new MysqlConnection());
>
> Anyone who is not familiar with std.parallelism and D's lazy parameter feature
> is going to be very surprised to find out what this code really does. This
> might be OK for us, experienced D users, but think about the poor bloke who
> will someday, somewhere try to debug a D program written by someone else, and
> tear his hair out trying to figure out why an expression passed as an argument
> to some function isn't being evaluated before/during the function call. (The
> solution I would suggest is simply having to specify the "lazy" keyword before
> the expression of each lazy parameter, same as C#'s "ref". This will require
> updating all usage of "enforce" among other changes.)
>
> [...current vote about std.parallel...]
>For the moment, I would suggest
> changing all lazy parameters which are evaluated in different contexts (outside
> of the said function) into delegates, and replacing their usage with delegate
> literals.

Sounds very good to me.

Denis
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