• akcom <CppCoder gmail.com> Jan 30 2006
• "Jarrett Billingsley" <kb3ctd2 yahoo.com> Jan 30 2006
• akcom <CppCoder gmail.com> Jan 30 2006
• Dave <Dave_member pathlink.com> Feb 01 2006

akcom <CppCoder gmail.com> writes:

If this has already been reported, I sincerely apologize;

class Foo
{
	int []arr;
	this()
	{
		arr = new int[12];
	}
	void Bar()
	{
		arr.length++;
		/+
		int len;
		len = arr.length;
		arr.length = len+1;
		+/
	}
}

in Foo.Bar(), the arr.length++ statement raises the following error in 
the compiler: "test.d(126): (this.arr).length is not an lvalue", but 
when using the commented code, everything compiles just fine

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"akcom" <CppCoder gmail.com> wrote in message 
news:drmdtk$1j7u$1 digitaldaemon.com...
 in Foo.Bar(), the arr.length++ statement raises the following error in the 
 compiler: "test.d(126): (this.arr).length is not an lvalue", but when 
 using the commented code, everything compiles just fine


At the very bottom of the "Properties" topic in the D spec, is this notice:

 Note: Properties currently cannot be the lvalue of an op=, ++, or --  
operator.

This is because properties are treated like functions.  So

arr.length++

Would be like writing

arr.length()++

Which doesn't make sense (it's a no-op).

Instead, you can write

arr.length = arr.length + 1 

akcom <CppCoder gmail.com> writes:

Jarrett Billingsley wrote:
 "akcom" <CppCoder gmail.com> wrote in message 
 news:drmdtk$1j7u$1 digitaldaemon.com...
 in Foo.Bar(), the arr.length++ statement raises the following error in the 
 compiler: "test.d(126): (this.arr).length is not an lvalue", but when 
 using the commented code, everything compiles just fine


 At the very bottom of the "Properties" topic in the D spec, is this notice:
 
  Note: Properties currently cannot be the lvalue of an op=, ++, or --  
 operator.
 
 This is because properties are treated like functions.  So
 
 arr.length++
 
 Would be like writing
 
 arr.length()++
 
 Which doesn't make sense (it's a no-op).
 
 Instead, you can write
 
 arr.length = arr.length + 1 
 
 

Dave <Dave_member pathlink.com> writes:

akcom wrote:
 If this has already been reported, I sincerely apologize;
 
 class Foo
 {
     int []arr;
     this()
     {
         arr = new int[12];
     }
     void Bar()
     {
         arr.length++;
         /+
         int len;
         len = arr.length;
         arr.length = len+1;
         +/
     }
 }
 
 in Foo.Bar(), the arr.length++ statement raises the following error in 
 the compiler: "test.d(126): (this.arr).length is not an lvalue", but 
 when using the commented code, everything compiles just fine


arr.length = arr.length + 1; // also legal

That is by design, and I think the general feeling is that the current 
semantics are correct because .length is not an lvalue - it's a property 
- so the prohibition against pre/post increment/decrement operators 
makes sense.

Take a look at the bottom of: http://digitalmars.com/d/property.html

It's also consistent with this:

import std.stdio;
void main()
{
     C c = new C;
//  c.i++;         // Error
     c.i = c.i + 1; // Ok
     writefln(c.i);
}
class C
{
     private int _i;
     int i() { return _i; }
     int i(int val) { return _i = val; }
}