Dictionary (index) initializers

C# language feature:

Dictionary (index) initializers

applies to

dictionaries, collections

benefit

Allows use of key/index during initialization. i.e. intialization is similar to usage.

how to use

Use key/index between [ and ] followed by = followed by initial value. Seperate with , if repeating multiple key/value initializations.

note

Index initializer may also be used with other collections such as List. However, traditional collection initialization are easier to express without “boiler plate” consecutive indexed assignments.

example:

        private Dictionary<int, string> webErrors = new Dictionary<int, string>
        {
            [401] = "Not authorized",
            [404] = "Page/Resource not found",
            [500] = "Internal server error"
        };

        // previously initialization would be declared with and object contianing key value objects seperated by comma
        private Dictionary<int, string> uglier_webErrors_initialization= new Dictionary<int, string>
        {
            {401 , "Not authorized" },
            {404 , "Page/Resource not found" },
            {500 , "Internal server error" }
        };

C# articles

csharp v2 +

Anonymous methods * Co- and Contra-variance for delegates * Delegate inference * Generics * Getter and setter separate accessibility * Iterators * Method group conversions (delegates) * Nullable types * Partials * Static classes *

csharp v3 +

Anonymous types * Auto-Implemented properties * Expression trees * Extension methods * Implicitly typed local variables * Lambda expression * Object and collection initializers * Partial methods * Query expressions *

csharp v4 +

Generic co- and contravariance * Named and optional arguments *

csharp v5 +

Asynchronous methods * Caller info attributes *

csharp v6 +

A note for CSharp 6 and beyond * Allow await in catch and finally blocks * Auto property initializers * Default values for Read-only Auto-properties * Dictionary (index) initializers * Exception filters * Expression-bodied members * Import of static type members into namespace * Null propagator (null-conditional operator, succinct null checking) * String interpolation * nameof operator *

csharp v7 +

Binary literals * Deconstruction * Digit separators * Expression bodied constructors and finalizers * Expression bodied getters and setters * Generalized async return types * Local functions * Out variables * Pattern matching * Ref returns and locals * Tuples *

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