How can we make it easier to experiment with the compiler?

[Basile B.]

On Thursday, 27 May 2021 at 08:41:49 UTC, Walter Bright wrote:
> On 5/27/2021 12:14 AM, Mathias LANG wrote:
>> Now to talk about what can be done to improve the DMD 
>> codebase, it's fairly obvious: ELIMINATE ALL CASTS. But not by 
>> replacing `cast(XXX)e` with `e.isXXX()`, but by actually using 
>> proper encapsulation.
>> 
>> What I mean is that instead of switching on types, like this:
>> ```D
>> if (auto tf = t.isTypeFunction())
>>      (cast(FunctionDeclaration)t.sym).something();
>> else if (auto td = t.isTypeDelegate())
>> (cast(FunctionDeclaration)(cast(TypeFunction)t).sym).something();
>> else
>>      // Something else
>> ```
>
> The isXXX() functions also make for safe casting.

And this is actually the only way to dyncast cast nodes as DMD 
AST is extern(C++)... But TBH I think that all the isXXX family 
of functions should be free functions, not members funcs. All 
these isXXX calls are virtuals but they dont need to (although 
often devirtualized).