On 05/16/2016 10:39 PM, Alex wrote:
// This function is intentionally templated, as it should take slices
and return something
// boundchecked only
@nogc T[] getSlice(T)(T* ptr, size_t a, size_t b)
{
return T[a .. b];
Typo here. Should be `ptr[a .. b]`.
}
void main()
{
void* ptr; // this will stay uninitialized during the whole program
run
The pointer is being initialized, though. To null, which is why your
shenanigans below work reliably.
// something that works as desired:
writeln(&ptr[4]); // prints '4'
auto b = getSlice(ptr, 5, 10);
writeln("b first: ", &b[0]); // prints '5'. This is the most useful
feature.
assert(b.capacity == 0); // holds always. So, getSlice returns
always a slice, not an array.
// arr[3] = ... // fails. It is intended to do so.
// something that does not worked as expected:
// how to rewrite a for loop
for(auto i = 0; i < b.length; i++) writeln(&b[i]);
// into a foreach loop?
Not, I guess, since you can't have a void variable, not even if it's
marked `ref`.
I have to say that I don't see the point in all this. You can't access
the elements of b in any way, since they're in memory that you don't
own. So all you got here is a fancy way of counting, no?
Looping over a range of numbers:
----
foreach (i; 5 .. 10) writeln(i);
----
Or if you want to store it in a variable:
----
import std.range: iota;
auto b = iota(5, 10);
foreach (i; b) writeln(i);
----
// a question about usability: is there a trait, which can
semantically check, if a type
// (void, or something else) behaves in the described manner?
Not sure what you mean here. What's the described manner? Not being able
to have a variable of the type?
I think void is the only type with that property. So maybe checking if
the type is exactly void is enough: `is(T == void)`.
Or you can check if some operation works on the type or a value of it:
`__traits(compiles, writeln(T.init))`
}
