Breaking Changes In Argument List Evaluation In C# 5.0

paulo — Wed, 18 Jul 2012 05:00:00 GMT

The C# Language Specification states on §7.5.1.2 that “(…) the expressions or variable references of an argument list are evaluated in order, from left to right (…)”.

So, when this code is compiled with the C# 4.0 compiler:

static void M(
    int x = 10,
    int y = 20,
    int z = 30)
{
    Console.WriteLine(
        "x={0}, y={1}, z={2}", x, y, z);
}

static void Main(string[] args)
{
    int a = 0;

    M(++a, z: ++a);
}

and run, this unexpected output is obtained:

x=2, y=20, z=1

In fact, fixing this compiler flaw was the cause of one of the few breaking changes introduced in C# 5.0.

Using the 5.0 compiler, the expected result is obtained:

x=1, y=20, z=2

To avoid this type of surprises, expression evaluation should be avoided in argument lists.

With this code:

int a = 0;

int i = ++a;
int j = ++a;

M(i, z: j);

the same result is obtained for both C# 4.0 and C# 5.0:

x=1, y=20, z=2

What Is The .NET Framework 4.5?

paulo — Mon, 17 Oct 2011 05:00:00 GMT

According to the .NET Blog, .NET Framework 4.5 is an in-place update that replaces .NET Framework 4.0 (rather than a side-by-side installation). The goal is for .NET 4.5 to be fully backward compatible with applications built for .NET 4.0 (.NET 3.5 and .NET 4.5 will be side-by-side).

One of the first things you’ll notice about .NET 4.5 is the version number of the CLR (4.0.30319) is the same as .NET 4.0; this is the practice used by other in-place updates. (read more)

In fact, if you compare a system with .NET 4.5 with a system with .NET 4.0 you’ll see that 4.5 is just an update to 4.0:

Registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full
Value	.NET 4.0	.NET 4.5
Version	4.0.30319	4.5.40805
CBS	1	1
TargetVersion	4.0.0	4.0.0
Install	1	1
Servicing	0	0
Release		368485
InstallPath	C:\Windows\Microsoft.NET\Framework64\v4.0.30319\	C:\Windows\Microsoft.NET\Framework64\v4.0.30319\

One of the major additions to the framework is the support for the Task-based Asynchronous Pattern. All classes with asynchronous APIs have be augmented with a Task-based asynchronous API.

Task exception handling has also changed in .NET 4.5 to accommodate the new async keywords in C# and VB. (read more)

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Breaking Changes In Argument List Evaluation In C# 5.0

What Is The .NET Framework 4.5?