`@safe` by default. What about `@pure` and `immutable` by default?

[Mike Franklin]

On Friday, 19 April 2019 at 21:46:20 UTC, Jonathan M Davis wrote:

>> We should be doing
>>
>> attr(true | false | null)
>>
>> three way!
>>
>>
>> But yeah, that's where I would focus too. Then your modules 
>> can opt in pretty easily.
>
> Definitely - though I'm not quite sure how allowing null would 
> work with allowing expressions that result in bool, which is 
> what we really should be doing rather than requiring an 
> explicit true or false. It can obviously be done, but I'm not 
> quite sure how that would be spec-ed out.

I think we could make it an enum:

enum AttributeState
{
     yes,
     no,
     infer
}

Then the compiler will take `pure(MyCoolExpression)` and rewrite 
it to `pure(_d_setAttributeState(MyCoolExpression))`.  In 
druntime we then implement an overloaded `AttributeState 
_d_setAttributeState(T)(T value)` to do the right thing.

The spec can say we allow any expression that evaluates to `bool` 
or `typeof(null)` at compile-time. `_d_setAttributeState`, 
through D's metaprogramming and design-by-introspection 
abilities, can implement the spec to translate a `bool` or 
`typeof(null)` expression to an `AttributeState` value.


Mike