scope(exit) considered harmful

[Jacob Carlborg]

On 11/8/09 11:46, Justin Johansson wrote:
> Long ago in the days before D, I was used to commenting out code with one of
> two idioms:
>
> #if false
> .. this code is not compiled
> #endif
>
> or
>
> if (false) {
> .. this code is compiled but not executed
> }
>
> and to turn stuff back on again:
>
> #if true
> .. this code is back on now
> #endif
>
> or
>
> if (true) {
> .. this code is back on now too
> }
>
> but in the D world beware the Ides of Scopes because if your curly
> brace block with the true/false conditional contains a scope(exit)
> you will get explainable but unexpected behaviour if this code
> is enabled inside an if(true) block.
>
> Gotcha.
>
> If scope(exit) is meant to be some mechanism for saving try/finally
> boiler-plate code, it is a can of worms, otherwise it is a can of
> i-dont-know-what-it's-good-for.
>
> To my way of thinking, and no doubt I should go back to remedial CS-101,
> semantics of scope(exit)  should related to function scope and not
> curly-brace scope-statement scope.
>
> Whilst an experienced coder (C/C++) and well understand what's
> happening here in D, I feel compelled to say that this would have
> to be a nightmare come true for newcomers to D.
>
> My advice, stick to try/catch/finally and avoid D scope(exit) et. al.
>
> -- Justin Johansson
>

The translation of "#if" to D is "static if" which does not introduce a 
new scope.