context-free grammar

[Peter Alexander]

On 5/03/11 4:39 AM, Jonathan M Davis wrote:
> On Friday 04 March 2011 20:31:38 Walter Bright wrote:
>> uri wrote:
>>> Explain why (a*b) is lvalue in bearophile's second example.
>>
>> Because the expression evaluates to a temporary, which is an lvalue.
>>
>>> This is one of the weird things in D. The language is too complex. It
>>> takes years to find out about the corner cases.
>>
>> It's not a weird corner case at all. Temporaries can be used as lvalues (in
>> C++ too).
>
> Really? I thought that a temporary was pretty much _the_ classic example of an
> rvalue. If you can assign to temporaries, you can assign to most anything then,
> other than literals. Why on earth would assigning to temporaries be permitted?
> That just seems unnecessary and bug-prone.
>
> - Jonathan M Davis

How do you think array assignments in C++ work?

a[i] = x;

a[i] is just *(a + i), i.e. the evaluation of an expression that yields 
a temporary, which in this case is an lvalue. Same applies to all other 
operator[] overloads.