proposed @noreturn attribute

[H. S. Teoh via Digitalmars-d]

On Sun, Jul 09, 2017 at 02:49:35PM -0400, Nick Sabalausky (Abscissa) via Digitalmars-d wrote:
> On 07/09/2017 06:51 AM, Daniel N wrote:
> > On Sunday, 9 July 2017 at 10:31:47 UTC, Mr.D wrote:
> > > On Saturday, 8 July 2017 at 10:15:39 UTC, Walter Bright wrote:
> > > 
> > > > Has anyone a better idea?
> > > 
> > > What about
> > > 
> > > scope(exit) assert(0);
> > > 
> > > ?
> > 
> > void func()
> > out { assert(0); }
> > body
> > {
> > }
> 
> Too indirect and verbose. An attribute or special "return type" would
> just cut straight to the case.

If DIP 1009 is accepted, this would not be verbose at all:

	void func()
	out(false) // it even tells you it won't return
	{
		...
	}

Plus, this has the advantage that you can specify a valid return type
for when you need to override a base class method, e.g.:

	class JitCompiler {
		Code compile(string code);
	}
	class InvalidCompiler : JitCompiler {
		override Code compile(string code) out(false) {...}
	}

A Bottom type that implicitly converts to anything would also fit the
bill, granted, but does require changing the language.

The main thing I have against adding a Bottom type is that it adds yet
another built-in type to the language, which means (1) a combinatorial
explosion of existing language constructs combined with the new type,
with currently-unknown consequences (and possibly corner cases we
haven't thought of that will come back to bite us), (2) yet another
special type newcomers have to learn with special semantics (I can
already anticipate complaints to D.learn about what's the difference
between null and bottom); (3) having to implement lots of compiler
changes to handle how this new type interacts with operators and other
types in all possible cases; (4) all of this just for something that (a)
is only rarely used, and (b) could have been easily implemented by
adding @noreturn or using existing contract syntax without adding a
whole new basic type to the language.

Honestly, I'd vote for @noreturn as the simplest, most straightforward
solution, and the only reason I'm arguing for out{assert(0);} (or
out(false) if DIP 1009 is accepted) is because people are all up in arms
about adding Gosh Yet Another Special UDA In Addition To The Numerous
Special UDAs We Already Have Like @safe and @nogc.


T

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