[Issue 10854] debug should also bypass safety and nothrow

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=10854



--- Comment #2 from monarchdodra at gmail.com 2013-08-19 10:40:40 PDT ---
(In reply to comment #1)
> (In reply to comment #0)
> 
> > debug instructions/blocks were allowed to nicely bypass function purity. This
> > allows inserting impure calls for testing reasons inside pure functions.
> > 
> > This should be expanded for @safe and nothrow. Its really a natural evolution
> > IMO.
> 
> If in module A you call a nothrow function F from module B, and you pre-compile
> module A with aggressive optimizations that rely on F never throwing, and then
> you run the module B in debug mode and now the function F throws, what does it
> happens?

If the *context* of the debug instruction is nothrow, then the debug could be
automatically expanded to try {BODY} catch (Exception e){assert(0,
format"Exception %s was thrown from a debug clause in a nothrow context");}

Or something with "scope(failure)", to avoid scoping the debug instruction/

> If F is also tagged with 'pure' and when you debug B you call something not
> pure, like printf(), inside the debug{}, the optimizations of the compilation
> of the module A could cause some of those calls to printf() to never happen.

But that is what we already have. Also, I don't think the new pure definitions
mean a pure function can be outright optimized out. But I'm unsure.

> But if the code inside debug{} is well behaved this doesn't cause significant
> problems. Peraphs with nothrow the situation is worse.
> 
> 
> > There is nothing more annoying than inserting a test "writeln()" in a function,
> > only to be refused because said function is @safe or nothrow.
> 
> For that I try to use printf(), that is nothrow.

That is indeed a workaround, but much less powerful than a writef. It is also a
workaround to something (IMO) you shouldn't have to. But thanks for the tip.

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