Argh!! Cyclic dependencies!!!

[Michel Fortin]

On 2011-03-18 19:24:41 -0400, Jason House <jason.james.house at gmail.com> said:

> Nick Sabalausky Wrote:
> 
>> These module constructor "Cyclic dependencies" errors are really starting to
>> piss me off. I feel like I'm back in the days when you'd sneeze and DMD
>> would vomit out 100 forward reference errors just because you didn't write
>> your whole damn app in one giant ultra-module. (/me takes a breather to
>> chill out...Ok...)
>> 
>> I don't suppose there's any chance we could get a quick little:
>> 
>> import foo;
>> 
>> pragma(staticCtorsAvoid, foo);
>> // Or
>> pragma(staticCtorsRunBefore, foo);
>> // Or
>> pragma(staticCtorsRunAfter, foo);
>> 
>> static this()
>> {
>> // do trivial shit that doesn't touch foo
>> }
>> 
> 
> Could module-level globals be treated like local variables to the 
> static constructor for the purpose of checking purity?
> 
> AKA
> static this() pure
> {
>   // trivial stuff
>   // calls weakly pure functions
>   // writes module-level globals
>   // reads module-level globals
>   // etc...
> }
> 
> 
> That's compiler enforceable and effectively means that stati 
> constructor does not count as part of a cyclic dependency...

That would work nicely, except for one thing: static constructors can 
be used to build immutable global variables. And pure functions have 
access to immutable global variables. This means two things:

1. purity isn't really guarantied for pure functions inside a module 
constructor
2. pure functions could access immutable global variables of other 
modules before their initialization

I think the pragma is a more viable solution, athough not very elegant.

-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/