Reference to an object disregarding mutation - what's the trick?

[Daniel Keep]

Your other problem's been addressed, but I just wanted to comment on

Steve Teale wrote:
> OK, so I'm in a typical tree situation:
> 
> int n = node.parent.nodelist.length;
> node.parent.nodelist.length = n+1;
>    // p.s. why can't I say node.parent.nodelist.length++ - doesn't work

This is probably one of big warts with properties in D.  An array's
".length" isn't just a data field.  Because assigning to it can cause
other things to happen (like a reallocation), it's a property.  And
because of the way properties are implemented in D, they cannot act as
lvalues.

Short version: You can't ++, --, op= a property, or pass it by reference.

If you're still wondering what the difference is:

struct LengthIsAField
{
    size_t length;
}

struct LengthIsAProperty
{
    size_t length() { ... }
    size_t length(size_t value) { ... }
}

Both are accessed using "instance.length", but the latter can't be used
as an lvalue.

Hope that helps :)

	-- Daniel

-- 
int getRandomNumber()
{
    return 4; // chosen by fair dice roll.
              // guaranteed to be random.
}

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