bottom type as parameter or local variable, does that make sense?

Timon Gehr timon.gehr at
Fri Jan 14 20:59:18 UTC 2022

On 1/14/22 19:32, H. S. Teoh wrote:
> On Fri, Jan 14, 2022 at 07:24:22PM +0100, Timon Gehr via Digitalmars-d wrote:
>> On 1/14/22 18:41, H. S. Teoh wrote:
>>> But in D, whenever a variable is declared, it gets initialized to
>>> its default value unless specified otherwise. Since nothing is
>>> specified here, it ought to perform its default initialization, and
>>> since there is no value with which it can be initialized, it ought
>>> to raise a runtime exception.
>> I don't follow why this is necessarily desirable. E.g., if generic
>> code checks whether or not a type can be default constructed, it will
>> by default get a spurious "yes" answer and has to special case
>> `noreturn`.
> ? Isn't that exactly what it should be?  If generic code checks whether
> type T can be default constructed, and T happens to be noreturn, then it
> would fail because noreturn.init is not constructible.

noreturn.init is assert(0), which compiles.

> Presumably, the
> code is doing this check because it's about to create a variable of type
> T afterwards, so returning "yes" would lead to instantiating noreturn
> variables. Why would that be a good thing?
> T

My point was the opposite of what you now seem to be taking it to be. 
You said there ought to be default initialization, which for noreturn is 
a runtime exception. I asked why this "ought" to be so.

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