Skip to main content

C# Brainteasers

I first saw this on Ayende's blog (in a rather more obscure form, admittedly). Once again, work out what will be printed, and why.

using System;

class Test
{
    static void Main()
    {
        Foo("Hello");
    }
   
    static void Foo(object x)
    {
        Console.WriteLine("object");
    }
   
    static void Foo<T>(params T[] x)
    {
        Console.WriteLine("params T[]");
    }
}

Answer: params T[] is printed. Now why would the compiler choose to create an array when it doesn't have to? Well... there are two stages to this. Firstly, when trying to find overloads which are legitimate candidates to be called, type inference works out that T should be System.String. Nothing scary so far.
Then overloading tries to work out which method is "better". If it's a choice between string x and params string[] x the former will always win - but at this point it's effectively a choice between object x andparams string[] x. (The fact that one is actually a generic method is only relevant in a tie-break situation.) For the purposes of working out "better conversions" the expanded form of the method with the paramsparameter is then used. This means that by the time actual conversions are considered, the choices are object x or string x - so clearly the latter wins.

Labels

Labels:

Comments

Post a Comment

Popular posts from this blog

gcAllowVeryLargeObjects Element

There are numerous new features coming with .NET 4.5 and here, on this blog, you can find several posts about it. But the feature we are goint to talk about today is very exciting, because we were waiting for it more than 10 years. Since .NET 1.0 the memory limit of .NET object is 2GB. This means you cannot for example create array which contains elements with more than 2GB in total. If try to create such array, you will get the OutOfMemoryException. Let’s see an example how to produce OutOfMemoryException. Before that Open Visual Studio 2012, and create C# Console Application, like picture below. First lets create simple struct with two double members like example below: 1 2 3 4 5 6 7 8 9 10 11 12 public struct ComplexNumber {      public double Re;      public double Im;      public ComplexNumber( double re, double im)      {    ...
Post a Comment
Read more

Support for debugging lambda expressions with Visual Studio 2015

Anyone who uses LINQ (or lambdas in general) and the debugger will quickly discover the dreaded message “Expression cannot contain lambda expressions”. Lack of lambda support has been a limitation of the Visual Studio Debugger ever since Lambdas were added to C# and Visual Basic.  With visual studio 2015 Microsoft has added support for debugging lambda expressions. Let’s first look at an example, and then I’ll walk you through current limitations. Example To try this yourself, create a new C# Console app with this code: using System.Diagnostics; using System.Linq; class Program { static void Main() { float[] values = Enumerable.Range(0, 100).Select(i => (float)i / 10).ToArray(); Debugger.Break(); } } Then compile, start debugging, and add “values.Where(v => (int)v == 3).ToArray()” in the Watch window. You’ll be happy to see the same as what the screenshot above shows you. I am using Visual Studio 2015 Preview and it has some limitati...
1 comment
Read more

An Introduction to Windows Azure Table Storage

Windows Azure Tables are a non-relational, key-value-pair, storage system suitable for storing massive amounts of unstructured data.  Whereas relational stores such as SQL Server, with highly normalized designs, are optimized for storing data so that queries are easy to produce, the non-relational stores like Table Storage are optimized for simple retrieval and fast inserts.  This article will cover the very basics of Windows Azure Table storage and provide you with resources and suggested topics to continue your learning. Some people, when first learning about the Windows Azure platform, find it hard to understand the purpose of the Table Storage feature.  This is especially true of those who are familiar with developing applications using highly relational data.  To get a good understanding of how a Key-Value Pair system differs from a traditional relational database you can read Buck Woody’s article on the topic in his continuing series:...
Post a Comment
Read more