问题
I'm interested: What is C#'s analog of std::pair in C++? I found System.Web.UI.Pair class, but I'd prefer something template-based.
Thank you!
回答1:
Tuples are available since .NET4.0 and support generics:
Tuple<string, int> t = new Tuple<string, int>("Hello", 4);
In previous versions you can use System.Collections.Generic.KeyValuePair<K, V> or a solution like the following:
public class Pair<T, U> {
public Pair() {
}
public Pair(T first, U second) {
this.First = first;
this.Second = second;
}
public T First { get; set; }
public U Second { get; set; }
};
And use it like this:
Pair<String, int> pair = new Pair<String, int>("test", 2);
Console.WriteLine(pair.First);
Console.WriteLine(pair.Second);
This outputs:
test
2
Or even this chained pairs:
Pair<Pair<String, int>, bool> pair = new Pair<Pair<String, int>, bool>();
pair.First = new Pair<String, int>();
pair.First.First = "test";
pair.First.Second = 12;
pair.Second = true;
Console.WriteLine(pair.First.First);
Console.WriteLine(pair.First.Second);
Console.WriteLine(pair.Second);
That outputs:
test
12
true
回答2:
System.Web.UI contained the Pair class because it was used heavily in ASP.NET 1.1 as an internal ViewState structure.
Update Aug 2017: C# 7.0 / .NET Framework 4.7 provides a syntax to declare a Tuple with named items using the System.ValueTuple struct.
//explicit Item typing
(string Message, int SomeNumber) t = ("Hello", 4);
//or using implicit typing
var t = (Message:"Hello", SomeNumber:4);
Console.WriteLine("{0} {1}", t.Message, t.SomeNumber);
see MSDN for more syntax examples.
Update Jun 2012: Tuples have been a part of .NET since version 4.0.
Here is an earlier article describing inclusion in.NET4.0 and support for generics:
Tuple<string, int> t = new Tuple<string, int>("Hello", 4);
回答3:
Unfortunately, there is none. You can use the System.Collections.Generic.KeyValuePair<K, V> in many situations.
Alternatively, you can use anonymous types to handle tuples, at least locally:
var x = new { First = "x", Second = 42 };
The last alternative is to create an own class.
回答4:
C# has tuples as of version 4.0.
回答5:
Some answers seem just wrong,
- you can't use dictionary how would store the pairs (a,b) and (a,c). Pairs concept should not be confused with associative look up of key and values
- lot of the above code seems suspect
Here is my pair class
public class Pair<X, Y>
{
private X _x;
private Y _y;
public Pair(X first, Y second)
{
_x = first;
_y = second;
}
public X first { get { return _x; } }
public Y second { get { return _y; } }
public override bool Equals(object obj)
{
if (obj == null)
return false;
if (obj == this)
return true;
Pair<X, Y> other = obj as Pair<X, Y>;
if (other == null)
return false;
return
(((first == null) && (other.first == null))
|| ((first != null) && first.Equals(other.first)))
&&
(((second == null) && (other.second == null))
|| ((second != null) && second.Equals(other.second)));
}
public override int GetHashCode()
{
int hashcode = 0;
if (first != null)
hashcode += first.GetHashCode();
if (second != null)
hashcode += second.GetHashCode();
return hashcode;
}
}
Here is some test code:
[TestClass]
public class PairTest
{
[TestMethod]
public void pairTest()
{
string s = "abc";
Pair<int, string> foo = new Pair<int, string>(10, s);
Pair<int, string> bar = new Pair<int, string>(10, s);
Pair<int, string> qux = new Pair<int, string>(20, s);
Pair<int, int> aaa = new Pair<int, int>(10, 20);
Assert.IsTrue(10 == foo.first);
Assert.AreEqual(s, foo.second);
Assert.AreEqual(foo, bar);
Assert.IsTrue(foo.GetHashCode() == bar.GetHashCode());
Assert.IsFalse(foo.Equals(qux));
Assert.IsFalse(foo.Equals(null));
Assert.IsFalse(foo.Equals(aaa));
Pair<string, string> s1 = new Pair<string, string>("a", "b");
Pair<string, string> s2 = new Pair<string, string>(null, "b");
Pair<string, string> s3 = new Pair<string, string>("a", null);
Pair<string, string> s4 = new Pair<string, string>(null, null);
Assert.IsFalse(s1.Equals(s2));
Assert.IsFalse(s1.Equals(s3));
Assert.IsFalse(s1.Equals(s4));
Assert.IsFalse(s2.Equals(s1));
Assert.IsFalse(s3.Equals(s1));
Assert.IsFalse(s2.Equals(s3));
Assert.IsFalse(s4.Equals(s1));
Assert.IsFalse(s1.Equals(s4));
}
}
回答6:
If it's about dictionaries and the like, you're looking for System.Collections.Generic.KeyValuePair<TKey, TValue>.
回答7:
Depending on what you want to accomplish, you might want to try out KeyValuePair.
The fact that you cannot change the key of an entry can of course be rectified by simply replacing the entire entry by a new instance of KeyValuePair.
回答8:
I created a C# implementation of Tuples, which solves the problem generically for between two and five values - here's the blog post, which contains a link to the source.
回答9:
I was asking the same question just now after a quick google I found that There is a pair class in .NET except its in the System.Web.UI ^ ~ ^ (http://msdn.microsoft.com/en-us/library/system.web.ui.pair.aspx) goodness knows why they put it there instead of the collections framework
回答10:
Since .NET 4.0 you have System.Tuple<T1, T2> class:
// pair is implicitly typed local variable (method scope)
var pair = System.Tuple.Create("Current century", 21);
回答11:
I typically extend the Tuple class into my own generic wrapper as follows:
public class Statistic<T> : Tuple<string, T>
{
public Statistic(string name, T value) : base(name, value) { }
public string Name { get { return this.Item1; } }
public T Value { get { return this.Item2; } }
}
and use it like so:
public class StatSummary{
public Statistic<double> NetProfit { get; set; }
public Statistic<int> NumberOfTrades { get; set; }
public StatSummary(double totalNetProfit, int numberOfTrades)
{
this.TotalNetProfit = new Statistic<double>("Total Net Profit", totalNetProfit);
this.NumberOfTrades = new Statistic<int>("Number of Trades", numberOfTrades);
}
}
StatSummary summary = new StatSummary(750.50, 30);
Console.WriteLine("Name: " + summary.NetProfit.Name + " Value: " + summary.NetProfit.Value);
Console.WriteLine("Name: " + summary.NumberOfTrades.Value + " Value: " + summary.NumberOfTrades.Value);
回答12:
On order to get the above to work (I needed a pair as the key of a dictionary). I had to add:
public override Boolean Equals(Object o)
{
Pair<T, U> that = o as Pair<T, U>;
if (that == null)
return false;
else
return this.First.Equals(that.First) && this.Second.Equals(that.Second);
}
and once I did that I also added
public override Int32 GetHashCode()
{
return First.GetHashCode() ^ Second.GetHashCode();
}
to suppress a compiler warning.
回答13:
The PowerCollections library (formerly available from Wintellect but now hosted on Codeplex @ http://powercollections.codeplex.com) has a generic Pair structure.
回答14:
Apart from custom class or .Net 4.0 Tuples, since C# 7.0 there is a new feature called ValueTuple, which is a struct that can be used in this case. Instead of writing:
Tuple<string, int> t = new Tuple<string, int>("Hello", 4);
and access values through t.Item1 and t.Item2, you can simply do it like that:
(string message, int count) = ("Hello", 4);
or even:
(var message, var count) = ("Hello", 4);
来源：https://stackoverflow.com/questions/166089/what-is-c-sharp-analog-of-c-stdpair