[Issue 5348] Variable Length Arrays

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=5348


timon.gehr at gmx.ch changed:

           What    |Removed                     |Added
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                 CC|                            |timon.gehr at gmx.ch


--- Comment #6 from timon.gehr at gmx.ch 2011-11-15 15:07:25 PST ---
(In reply to comment #5)
> Currently this works, and ct_function() is run at compile-time because fixed
> array length definitions is a compile-time context, so in D it forces CTFE:
> 
> 
> int ct_function(int x) {
>     return x * 2;
> }
> void main() {
>     int[ct_function(5)] a;
> }
> 
> 
> If VLA come in D, and if their definition syntax is the same as the current
> fixed array definition syntax, then that length definition stops being a
> compile-time context, and the compiler is not forced (but free any way) to run
> ct_function() at compile-time.

It is not necessarily able to solve the particular halting problem instance.
The best that could be done without breaking backwards compatibility would be
to define the semantics of

int[foo()] a;

as either:

if foo() can be executed at compile time, take the result as the array length,
else either don't terminate compilation or introduce a VLA.

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