[C #6] 7-index initiator,

[C #6] 7-index initiator,
0. Directory

C #6 Add feature catalog

1. Old Version code

1 private static void Main()2 {3     var dictionary = new Dictionary<int, string> {4         { 1, "Value1" },5         { 2, "Value2" },6         { 3, "Value3" }7     };8 }

The Set initialization tool introduced in C #3, but let's use the above syntax to initialize some items when declaring a dictionary or set, in fact, in C #3, this is a syntactic sugar. The actual compiled result is to call the Add method of the dictionary or set to Add these items one by one. But it is a little inintuitive. Let's take a look at this version of IL:

 1 .method private hidebysig static void  Main() cil managed 2 { 3   .entrypoint 4   // Code size       47 (0x2f) 5   .maxstack  4 6   .locals init ([0] class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string> dictionary) 7   IL_0000:  nop 8   IL_0001:  newobj     instance void class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string>::.ctor() 9   IL_0006:  dup10   IL_0007:  ldc.i4.111   IL_0008:  ldstr      "Value1"12   IL_000d:  callvirt   instance void class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string>::Add(!0,13                                                                                                                 !1)14   IL_0012:  nop15   IL_0013:  dup16   IL_0014:  ldc.i4.217   IL_0015:  ldstr      "Value2"18   IL_001a:  callvirt   instance void class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string>::Add(!0,19                                                                                                                 !1)20   IL_001f:  nop21   IL_0020:  dup22   IL_0021:  ldc.i4.323   IL_0022:  ldstr      "Value3"24   IL_0027:  callvirt   instance void class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string>::Add(!0,25                                                                                                                 !1)26   IL_002c:  nop27   IL_002d:  stloc.028   IL_002e:  ret29 } // end of method Program::Main

Essentially, the call to the Add method. C #6 introduces a new method to further optimize this method.

2. Index initializer

1 private static void Main()2 {3     var dictionary = new Dictionary<int, string>4     {5         [1] = "Value1",6         [2] = "Value2",7         [3] = "Value3"8     };9 }

It looks much more intuitive, but it is actually a syntax improvement. The compilation results are also slightly different, as shown below:

 1 .method private hidebysig static void  Main() cil managed 2 { 3   .entrypoint 4   // Code size       47 (0x2f) 5   .maxstack  4 6   .locals init ([0] class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string> dictionary) 7   IL_0000:  nop 8   IL_0001:  newobj     instance void class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string>::.ctor() 9   IL_0006:  dup10   IL_0007:  ldc.i4.111   IL_0008:  ldstr      "Value1"12   IL_000d:  callvirt   instance void class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string>::set_Item(!0,13                                                                                                                      !1)14   IL_0012:  nop15   IL_0013:  dup16   IL_0014:  ldc.i4.217   IL_0015:  ldstr      "Value2"18   IL_001a:  callvirt   instance void class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string>::set_Item(!0,19                                                                                                                      !1)20   IL_001f:  nop21   IL_0020:  dup22   IL_0021:  ldc.i4.323   IL_0022:  ldstr      "Value3"24   IL_0027:  callvirt   instance void class [mscorlib]System.Collections.Generic.Dictionary`2<int32,string>::set_Item(!0,25                                                                                                                      !1)26   IL_002c:  nop27   IL_002d:  stloc.028   IL_002e:  ret29 } // end of method Program::Main

The main difference is that the old syntax is to call the Add method, and the new syntax is the set accesser (set_Item) of the indexer ).

Since it is an index, the index is not only int, but also string, any custom type.

3. Example

Namespace csharp6 {internal class Program {public class Person {public string Name {get; set;} public int Age {get; set;} private Dictionary <string, address >_cache = new Dictionary <string, Address> (); public Address this [string name] {get {return _ cache [name];} set {_ cache [name] = value ;}} public class Address {public string Name {get; set;} public string Zip {get; set ;}} private static void Main () {// string index var colorMap = new Dictionary <string, ConsoleColor> {["Error"] = ConsoleColor. red, ["Information"] = ConsoleColor. yellow, ["Verbose"] = ConsoleColor. white}; // enumeration index var colors = new Dictionary <ConsoleColor, string> {[ConsoleColor. red] = "# F00", [ConsoleColor. green] = "#0F0",}; // The custom type of index supports Person person = new Person {Name = "blackheart", Age = 1, ["home"] = new Address {Name = "Beijing", Zip = "100000"}, ["work"] = new Address {Name = "Nanjing ", zip = "200000" }}; // custom-type index var persons = new Dictionary <Person, List <Address> {[new Person {Name = "blackheart ", age = 1}] = new List <Address> {new Address {Name = "Beijing", Zip = "100000" }}, [new Person {Name = "blackheart ", age = 1}] = new List <Address> {new Address {Name = "Nanjing", Zip = "200000 "}},};}}}

4. Summary

In essence, the syntax [xxx] = yyy can be of any type and can be used for any type supported by the index. Simple and straightforward.