Optional tags and attributes

[Rikki Cattermole]

On Saturday, 18 January 2014 at 00:32:53 UTC, Stanislav Blinov 
wrote:
> On Saturday, 18 January 2014 at 00:23:14 UTC, Adam D. Ruppe 
> wrote:
>> Templates automatically infer their attributes based on the 
>> input, so you don't have to specify them there.
>>
>> If you do a foo!(nothrow_function)(), foo is also nothrow 
>> (unless, of course, it throws!)
>
> This doesn't apply here. I'm not using function as a template 
> paramter.
>
> That's the whole case here. Suppose I'm writing a template 
> class that's parametrized by some type, and in my method I want 
> to call methods of that type. I cannot make any of my functions 
> nothrow until I am sure the methods I call will not throw, and 
> the compiler will tell me. And how can I be sure they don't 
> throw if it's an arbitrary type? I can check it, sure, with 
> that isNoThrow() template. But how then to use that information 
> in my own function declaration?

Perhaps using template if statements and pure functions. A little 
like how I implemented some of Dvorm's[0] utility functions. That 
way it can execute at compile time. You can pass the type to it 
and check any method you would call if its nothrow or not via 
traits.
That way you can have two declarations but with one being 
opposite of the if.

[0] 
https://github.com/rikkimax/Dvorm/blob/master/src/orm/util.d#L31