State of the Compiler

[Jonathan M Davis via Digitalmars-d]

On Tuesday, 1 March 2016 at 13:48:18 UTC, Andrei Alexandrescu 
wrote:
> On 02/28/2016 11:57 PM, Walter Bright wrote:
>> There are good reasons for that. But there's no reason why
>> std.algorithm.sort, for example, cannot still be used (cut & 
>> paste).
>
> How would cutting and pasting from phobos be better than using 
> it? -- Andrei

You avoid a circular dependency. If it's just stuff like the 
functions in std.algorithm, it's probably not too bad, but if 
anything pulls in std.conv, std.format, std.stdio, etc., you end 
up with a bunch of extra stuff, whereas what the compiler really 
needs is probably only a small piece of that. And if there's a 
bug in any of the Phobos code that the compiler uses, you end up 
with a bug in the compiler, which in turn causes bugs when 
compiling Phobos...

Copying specific pieces of Phobos and pasting them into dmd does 
allow for stuff that's more specific to what dmd is doing and 
avoids dependency issues - but it does mean copying, which means 
code duplication and can cause it's own set of problems.

I don't know if it's ultimately better to have dmd use Phobos or 
not, but it does avoid some potentially weird dependency issues 
with bugs if we avoid it. Things already get weird enough when 
Phobos depends on itself. Locking the version down like Ola 
Fosheim Grøstad is talking about definitely would mitigate the 
problem, but it would just be simpler to avoid it. Regardless, 
I'll leave it up to the compiler devs to come to a decision on 
that one.

- Jonathan M Davis