bool (was DConf 2019 AGM Livestream)

Walter Bright newshound2 at
Sun May 12 05:43:01 UTC 2019

On 5/11/2019 7:27 PM, Mike Franklin wrote:
> I think Walter is conflating how bool is stored in memory with its 
> semantics.

That's exactly what I'm deliberately doing.

> I'm currently considering using D's rich modeling features 
> to create a new boolean type that behaves more like a boolean and less 
> like a bit.  But it's unfortunate and disappointing we have to resort to 
> something like that.

I understand. Every programmer, sooner or later, decides to step up and 
take a swing at inventing boolean. (I have too - did you know that D 
used to have a `bit` builtin type?) The programming landscape is 
littered with the corpses of one after another. Phobos has multiple ones 
- RefCountedAutoInitialize .yes and .no, and even a struct Yes and a 
struct No. std.bitmanip has an enum A{True,False}. std.json has enum 
E{True=true}. std.typecons has the bizarre enum 
issue10647_isAlwaysTrue=true;. (One wonders what would happen if it was 
set to false. Would it cause a rip in the fabric of space-time? I dare 
not experiment with that!)

The C++ Committee currently is fiercely debating adding a "Boolean" 
construct in one of the longest threads I've ever seen. One of their 
problems is it conflicts with the endless "Boolean" types added to 
existing C++ code, along with every variation "Bool", "Bool", "boolean", 

All this effort strongly implies that there's no such thing as a 
satisfactory bool type. Will you succeed where 10,000 other programmers 
have failed? Seems unlikely. But I doubt I will dissuade you from trying.

So what does work reasonably? Treating it like a small integer. We know 
what the various integer semantics are, and it fits right in with that. 
I know the operator ++ difference, and it is my fault that I succumbed 
to a moment of boolean madness and allowed that in. (++ on D bool is 
saturation arithmetic, unlike the overflow semantics in every other 
integer type. It is a mistake, please don't use that as justification 
for adding more quirky behaviors.)

On a final note, C++ added a std::vector<bool> special case, which works 
unlike any other vector type. Years of experience have shown that to 
have been a mistake, just like all the others, and it is widely derided 
as a complete failure.

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