18.02.2012 2:50, H. S. Teoh пишет:
> ...
You cannot have ref local variable, so e is a copy in any case. It may be a class reference or a pointer, so calling potentially non-const methods is probably not safe here, but assignment shouldn't give you problems.

On Sat, Feb 18, 2012 at 05:19:52AM +0200, Mantis wrote:
> 18.02.2012 2:50, H. S. Teoh пишет:
> >...
> You cannot have ref local variable, so e is a copy in any case. It may be a class reference or a pointer, so calling potentially non-const methods is probably not safe here, but assignment shouldn't give you problems.

But that's the problem, if e is a dynamic array, then it can potentially be modified through the original reference after being assigned.

Ideally, I'd need e to be a reference to an immutable type. But that requires a way of converting an arbitrary type to its immutable form, which I don't know how to do in a generic way.


T

-- 
Let's eat some disquits while we format the biskettes.

18.02.2012 7:51, H. S. Teoh пишет:
> On Sat, Feb 18, 2012 at 05:19:52AM +0200, Mantis wrote:
>> 18.02.2012 2:50, H. S. Teoh пишет:
>>> ...
>> You cannot have ref local variable, so e is a copy in any case. It
>> may be a class reference or a pointer, so calling potentially
>> non-const methods is probably not safe here, but assignment
>> shouldn't give you problems.
> But that's the problem, if e is a dynamic array, then it can potentially
> be modified through the original reference after being assigned.
>
> Ideally, I'd need e to be a reference to an immutable type. But that
> requires a way of converting an arbitrary type to its immutable form,
> which I don't know how to do in a generic way.
>
>
> T
>
I see. But you can't have a generic copy operation either, due to possibly complicated memory model of your program. You'd need a proper copy construction for that, but there is no way to check for it's correctness in generic type. I'd just use constraint to limit a range underlying type to immutable, something like:

template isImmutable(T) {
    static if( is( T == immutable T ) ) {
        enum isImmutable = 1;
    } else {
        enum isImmutable = 0;
    }
}
...
if( isImmutable!(ElementType!T) )
...

On Sat, Feb 18, 2012 at 08:02:15AM +0200, Mantis wrote:
> 18.02.2012 7:51, H. S. Teoh пишет:
> >On Sat, Feb 18, 2012 at 05:19:52AM +0200, Mantis wrote:
> >>18.02.2012 2:50, H. S. Teoh пишет:
> >>>...
> >>You cannot have ref local variable, so e is a copy in any case. It may be a class reference or a pointer, so calling potentially non-const methods is probably not safe here, but assignment shouldn't give you problems.
> >But that's the problem, if e is a dynamic array, then it can potentially be modified through the original reference after being assigned.
> >
> >Ideally, I'd need e to be a reference to an immutable type. But that requires a way of converting an arbitrary type to its immutable form, which I don't know how to do in a generic way.
[...]
> I see. But you can't have a generic copy operation either, due to possibly complicated memory model of your program. You'd need a proper copy construction for that, but there is no way to check for it's correctness in generic type.

True.


> I'd just use constraint to limit a range underlying type to immutable, something like:
> 
> template isImmutable(T) {
>     static if( is( T == immutable T ) ) {
>         enum isImmutable = 1;
>     } else {
>         enum isImmutable = 0;
>     }
> }
> ...
> if( isImmutable!(ElementType!T) )
> ...

Hmm. But the problem is that I want to be able to handle something like File.byLine(). Or perhaps what I really need is just to write a wrapper around File.readln() that ensures immutability, then I can use isImmutable() to enforce safety in the algorithm, and just pass the wrapper when I need to use an underlying File.


T

-- 
MAS = Mana Ada Sistem?

On Friday, February 17, 2012 22:27:06 H. S. Teoh wrote:
> Hmm. But the problem is that I want to be able to handle something like File.byLine(). Or perhaps what I really need is just to write a wrapper around File.readln() that ensures immutability, then I can use isImmutable() to enforce safety in the algorithm, and just pass the wrapper when I need to use an underlying File.

If you need to handle arrays differently, then just use a static if to specialize the appropriate section of code for them. So, something like

ElementType!R choose(R, E)(R range)
    if(isInputRange!R)
{
    Unqual!(ElementType!R) e;

    foreach(e; range)
    {
        if(/* some criterion */)
        {
            static if(isDynamicArray!(ElementType!R) &&
                      is(Unqual!(ElementType!R) == ElementType!R))
            {
                e = range.front.dup;
            }
            else
                e = range.front;
        }
    }

    return cast(ElementType!R)e;
}

- Jonathan M Davis