Unexpected range assignment behaviour

[matheus]

On Friday, 19 July 2024 at 15:33:34 UTC, Dennis wrote:
> On Friday, 19 July 2024 at 09:34:13 UTC, Lewis wrote:
>> But the value of $ here is 3. Why do I get a RangeError at 
>> runtime even though the slice is the correct size (and the 
>> same size as the hardcoded one that works)?
>
> The range `0 .. 3` has compile time known length, so it gets 
> converted to string[3]:
>
> ```D
> lookup["test"] = dynArray[0 .. 3];
> // becomes
> lookup["test"] = cast(string[3]) dynArray[0 .. 3];
> ```
>
> The key "test" doesn't exist yet, but because it's an 
> assignment, it gets created.
> However, `0 .. $` depends on a run-time variable here, so it 
> doesn't convert to a static array and does slice assignment:
>
> ```D
> lookup["test"] = dynArray[0 .. $];
> // becomes
> lookup["test"][0 .. $] = dynArray[0 .. $];
> ```
>
> Now, you get a range error because "test" doesn't exist in 
> `lookup`, and slice assignment doesn't create a new entry.

Hi Dennis, I undestood your explanation, and based on that  
couldn't this case for example be caught during the compiling 
time?

Thanks,

Matheus.