ref const array error

[jdrewsen]

On Wednesday, 18 January 2012 at 19:43:52 UTC, Timon Gehr wrote:
> On 01/18/2012 08:31 PM, jdrewsen wrote:
>> Recently the encoding.safeDecode stopped working for some of 
>> my existing
>> code. This example outlines the issue:
>>
>> import std.encoding;
>>
>> void main(string[] args) {
>> auto e = EncodingScheme.create("utf-8");
>> auto a = new byte[100];
>> e.safeDecode(a);
>> }
>>
>> Results in:
>>
>> Error: function std.encoding.EncodingScheme.safeDecode (ref
>> const(ubyte)[] s) const is not callable using argument types 
>> (byte[])
>>
>> Isn't this an error in the compiler?
>>
>> /Jonas
>>
>
> No, this is a bugfix. The operation is unsound:
>
> immutable(ubyte)[] foo(ref const(ubyte)[] s){
>    auto r = new immutable(ubyte)[1];
>    s = r;
>    return r;
> }
>
> void main() {
>    ubyte[] x;
>    immutable(ubyte)[] y = foo(x);
>    static assert(is(typeof(y[0])==immutable));
>    auto oldy0 = y[0];
>    x[0]=oldy0+1;
>    assert(oldy0 == y[0]); // fail
> }
>
> The functionality is not going away; You will be able to use 
> inout for the same purpose once my enhancement request gets 
> implemented: http://d.puremagic.com/issues/show_bug.cgi?id=7105

Wouldn't a nicer solution be to let the compiler ensure that
an immutable array cannot escape through a ref const array 
parameter?

/Jonas