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

[Seb]

On Friday, 19 April 2019 at 12:23:08 UTC, Andrei Alexandrescu 
wrote:
> On 4/15/19 11:59 PM, Mike Franklin wrote:
>> I think I may have found a simple migration path to @safe by 
>> default.  I'm still thinking it through, but if I can justify 
>> it, I will write a DIP.
>> 
>> `@safe` by default is a no-brainer in my opinion, but `pure` 
>> and `immutable` by default are less obvious.  With the 
>> aforementioned potential DIP, I have an opportunity to correct 
>> purity and mutability defaults as well...but is that something 
>> we want to do?
>> 
>> Can anyone save me some trouble and articulate why it would be 
>> bad to have `pure` and/or `immutable` by default?
>> 
>> Thanks,
>> Mike
>
> I haven't participated much to this but here's a thought. This 
> migration is again in the category "let's change things and 
> evaluate the costs". It is so much better to go with "let's add 
> and enjoy the benefits".

Most D code is yet to be written. Safe by default is sth. that 
all new D code should be

> It's cheap to make @safe and pure the defaults for a given 
> module. Plant this at the beginning:
>
> pure: @safe:

NOPE. That doesn't work as DMD doesn't set pure for member 
functions.

---
pure:

struct Foo {
     int bar() { return 42; }
}

void main()
{
    Foo().bar(); // Error: pure function D main cannot call impure 
function onlineapp.Foo.bar
}
---


https://run.dlang.io/is/cgESWs