A Philosophy of Software Design

[Richard (Rikki) Andrew Cattermole]

On 30/06/2026 7:49 AM, Walter Bright wrote:
> On 6/29/2026 1:05 AM, Richard (Rikki) Andrew Cattermole wrote:
>> But you can also throw static analysis at it to catch royally stupid 
>> cases like so:
>>
>> ```d
>> void thing(float arg) {
>>      float f;
>>
>>      return f + arg * 2;
>> }
>> ```
> 

I just noticed that is void and should be float oops.

> Default initializing f to nan catches it and propagates the error. 
> Default initialization to 0 does not.

At _runtime_ yes.

But it shouldn't get that far for royally stupid code like this.

Due to:

1. NaN like this should be considered to be a poison value, that will 
optimize _any_ expression that touches it by a modern backend.

2. It will NEVER do something useful at runtime. It will always a be a 
bug in the code, due to not initializing or not knowing that it is NaN 
not 0.

3. Failing to compile for 100% bad code is always better than runtime 
bad data. Even if it is a sentinel like NaN.

ldc -O:

```d
float thing(float arg) {
     float f;
     return f + arg * 2;
}

float another(float arg) {
     return thing(arg) + 2;
}
```

```
.LCPI0_0:
         .long   0x7fc00000
float example.thing(float):
         movss   xmm0, dword ptr [rip + .LCPI0_0]
         ret

.LCPI1_0:
         .long   0x7fc00000
float example.another(float):
         movss   xmm0, dword ptr [rip + .LCPI1_0]
         ret
```