new and operator ++

[Kerneltrap]

Hi,

I have a type:

public struct Value
{
public static Value operator ++(Value v)
{
return new Value();
}

public static Value New()
{
return new Value();
}
}

This code

Value v1 = Value.New()++;

compiles successfully, but i get InvalidProgramException.

The same for

Value v = new Value()++;

Changing from struct to class doesn't help.

Microsoft (R) Visual C# 2005 Compiler version 8.00.50727.42
Win XP SP2.

 

[Nicholas Paldino [.NET/C# MVP]]

This is pretty interesting, as I get the same thing (and one would
assume that the C# compiler wouldn't produce invalid code).

I would submit this to Microsoft Connect as a bug.

 

[Tom Spink]

Hi,

I have a type:

public struct Value
{
public static Value operator ++(Value v)
{
return new Value();
}

public static Value New()
{
return new Value();
}
}

This code

Value v1 = Value.New()++;

compiles successfully, but i get InvalidProgramException.

The same for

Value v = new Value()++;

Changing from struct to class doesn't help.

Microsoft (R) Visual C# 2005 Compiler version 8.00.50727.42
Win XP SP2.

Hi

JOOI, the Mono C# Compiler yields a compilation error:

"error CS0131: The left-hand side of an assignment must be a variable, a
property or an indexer"

Interesting.

 

[Willy Denoyette [MVP]]

Hi

JOOI, the Mono C# Compiler yields a compilation error:

"error CS0131: The left-hand side of an assignment must be a variable, a
property or an indexer"

Interesting.

This is actually what the C# compiler should do as well, this is a compiler
error that is corrected in Orcas version of the compiler.

Willy.

 

[Peter Duniho]

[...]
This code

Value v1 = Value.New()++;

compiles successfully, but i get InvalidProgramException.

The same for

Value v = new Value()++;

JOOI, the Mono C# Compiler yields a compilation error:

"error CS0131: The left-hand side of an assignment must be a variable, a
property or an indexer"

This is actually what the C# compiler should do as well, this is a
compiler error that is corrected in Orcas version of the compiler.

Okay, I'll bite.

Why is "Value v1" and "Value v" not considered a "variable, a property or
an indexer"? Specifically, sure looks like a variable to me. What am I
missing?

Pete

 

[Ben Voigt [C++ MVP]]

[...]
This code

Value v1 = Value.New()++;

compiles successfully, but i get InvalidProgramException.

The same for

Value v = new Value()++;

JOOI, the Mono C# Compiler yields a compilation error:

"error CS0131: The left-hand side of an assignment must be a variable, a
property or an indexer"

This is actually what the C# compiler should do as well, this is a
compiler error that is corrected in Orcas version of the compiler.

Okay, I'll bite.

Why is "Value v1" and "Value v" not considered a "variable, a property or
an indexer"? Specifically, sure looks like a variable to me. What am I
missing?

Pete


You're missing operator binding: The code reads as:

Value v = ((new Value())++);

The postincrement operator is buried within the right-hand side of the
assignment.

Does

Value v; (v = new Value())++;

work?

 

[Kerneltrap]

Kerneltrap wrote:
[...]
This code
Value v1 = Value.New()++;
compiles successfully, but i get InvalidProgramException.
The same for
Value v = new Value()++;
JOOI, the Mono C# Compiler yields a compilation error:
"error CS0131: The left-hand side of an assignment must be a variable, a
property or an indexer"

This is actually what the C# compiler should do as well, this is a
compiler error that is corrected in Orcas version of the compiler.

Okay, I'll bite.

Why is "Value v1" and "Value v" not considered a "variable, a property or
an indexer"? Specifically, sure looks like a variable to me. What am I
missing?

Pete

You're missing operator binding: The code reads as:

Value v = ((new Value())++);

The postincrement operator is buried within the right-hand side of the
assignment.

Does

Value v; (v = new Value())++;

work?

It doesn't. Same effect.

 

[Christof Nordiek]

Okay, I'll bite.

Why is "Value v1" and "Value v" not considered a "variable, a property or
an indexer"? Specifically, sure looks like a variable to me. What am I
missing?

What you're missing is, that exp++ contains an assignment to exp. So this
should be "a varialbe, a property or an indexer".

What actually do you wan't to do?

Christof

 

[Willy Denoyette [MVP]]

[...]
This code

Value v1 = Value.New()++;

compiles successfully, but i get InvalidProgramException.

The same for

Value v = new Value()++;

JOOI, the Mono C# Compiler yields a compilation error:

"error CS0131: The left-hand side of an assignment must be a variable, a
property or an indexer"

This is actually what the C# compiler should do as well, this is a
compiler error that is corrected in Orcas version of the compiler.

Okay, I'll bite.

Why is "Value v1" and "Value v" not considered a "variable, a property or
an indexer"? Specifically, sure looks like a variable to me. What am I
missing?

Pete



Pete, In top of what others said, the Mono compiler's error CS0131: is
somewhat misleading.
Orcas C# compiler error message:
[error CS1059: The operand of an increment or decrement operator must be a
variable, property or indexer]
is IMO more clear and accurate.


Willy.

 

[Peter Duniho]

Pete, In top of what others said, the Mono compiler's error CS0131: is
somewhat misleading.
Orcas C# compiler error message:
[error CS1059: The operand of an increment or decrement operator must be
a variable, property or indexer] is IMO more clear and accurate.

Ah, okay. Since ++ has an implicit assignment, the result has to be able
to be assigned back to the original source, which isn't possible in this
case.

Thanks everyone. Makes sense now.

Pete

 

[Tom Spink]

This is actually what the C# compiler should do as well, this is a
compiler error that is corrected in Orcas version of the compiler.

Willy.

Nice. I figured as much, because of postfix increment's implicit
assignment. It's a shame it's worded a bit funny in gmcs.

 

[cody]

This is pretty interesting, as I get the same thing (and one would
assume that the C# compiler wouldn't produce invalid code).

I would submit this to Microsoft Connect as a bug.

Strange.

Decimal d = New Decimal()++;

or even

Decimal d = 0m++;

Produces just a compilation error as it should. What is the difference?
Decimal is just a struct like any other or is it treated special by the
compiler as it is with System.String?