On Wed, 16 Dec 2009 14:43:47 -0500, Michel Fortin
<michel.for...@michelf.com> wrote:
On 2009-12-16 14:02:35 -0500, "Steven Schveighoffer"
<schvei...@yahoo.com> said:
On Wed, 16 Dec 2009 09:21:16 -0500, Michel Fortin
<michel.for...@michelf.com> wrote:
Here's what I meant:
void doSomething(inout(MyStruct)*[] a, inout(MyStruct)*[] b) {
a[0] = b[0]; // works only when structs in both arrays have the
same constness.
}
This is dangerous.
We should figure out a reason why this shouldn't compile. It's hard
for me to wrap my head around it. Either the implicit cast when
calling the function shouldn't work, or the assignment shouldn't work.
My intuition is that the implicit cast should fail.
If you're trying to define a ruke it's simple: you can cast immutable to
const only on the first level of indirection, or when there is no
indirection. So basically those conversions should be allowed:
immutable(MyStruct)*[] -> const(MyStruct*)[]
immutable(MyStruct*)[] -> const(MyStruct*)[]
immutable(MyStruct*[]) -> const(MyStruct*[])
That sounds correct.
Does this code compile today? If so, we need to fix this. With this
fixed, the inout version naturally becomes invalid.
Just did a couple of small tests. Apparently everything is all right:
test.d(18): Error: cannot implicitly convert expression (a) of type
immutable(int)*[] to const(int)*[]
Also:
test.d(18): Error: cannot implicitly convert expression (b) of type
int*[] to const(int)*[]
Which is right otherwise you could assign immutable values to the array
others see as mutable. Also, converting from immutable(int)*[] to
const(int*)[] implicitly works fine and does prevent dangerous
assignments.
So I don't think there is anything to fix on this front.
I did some testing too. This compiles, which should be a bug:
import std.stdio;
void myfunc(const(int)[][]a, const(int)[][]b)
{
a[0]= b[0];
}
void main()
{
immutable(int)[][] i1;
i1.length = 1;
int [][]i2;
i2 ~= [5];
myfunc(i1, i2);
writefln("%d", i1[0][0]);
i2[0][0] = 6;
writefln("%d", i1[0][0]);
}
Writes:
5
6
I think it has something to do with array casting rules. Because you can
cast just the pointer part of the array struct, it appears that these
cases aren't considered the same as the pointer casting as you
demonstrated.
I'll look for a bug on this, and if not, I'll add one.
-Steve
