When is a dynamic array really a static array?
belka at caraus.de
Tue Dec 31 11:51:26 UTC 2019
On Tuesday, 31 December 2019 at 11:20:31 UTC, Patrick Schluter
> On Monday, 30 December 2019 at 18:17:31 UTC, Steven
> Schveighoffer wrote:
>> On 12/30/19 11:45 AM, MoonlightSentinel wrote:
>>> Digger blames https://github.com/dlang/dmd/pull/4779
>>> This is probably a bug but DMD sometimes detects when the
>>> sliced array is static and uses this information to enable
>>> certain rewrites IIRC, e.g. when initializing another static
>> Thanks for everyone's replies:
> Is it really a bug?
> A static array is an array where the compiler handles the
> pointer/length structure (i.e. they are known at CT) vs a
> dynamic array, where it is a runtime variable. In contexts
> where the compiler can deduce completely the type (lifetime of
> the values) it can be justified to make CT values out of them.
> While I understand that it can be surprizing that the passed
> dynamic array becomes a static array again, it is imho only a
> sign that the compiler was able to deduce completely the
> lifetime of the passed object.
> I'm sure it is a good thing even if it might be surprizing in
> some contexts, but it is in the vein of the basic idea behind
> the D language to try to resolve things at CT when possible.
> Just my 2 cents.
It is inconsistent. The compiler can't just do whatever it wants.
If typeof(x) says that the type is char, then the type should
be char. How am I supposed to reason about the code if I don't
even know the types of my variables, and what overloads are
called? There should be strict coercion rules and there is no
such rule for converting a dynamic array to a static one just
because the compiler knows. And it changes the behaviour if the
variable is used in one of the templates.
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