C# - is: Cast Examples - Dot Net Perls

Is-keyword. This C# cast returns true if it succeeds. It returns false if the cast fails. This operator can be used to capture a cast variable.

This operator is useful when checking types in if-statements and expressions. We can use "is" for pattern-matching—it can capture the cast value.

case

Cast

Example. The is-operator is used to create an expression. It returns a boolean result of true or false. This is compatible with the if-statement, which requires a boolean context.

Info The is-operator evaluates the entire class derivation chain when it is applied. The string is both an object and string.

Here The first 2 if-statement bodies are reached. Their expressions are evaluated to the true value: the casts succeed.

Then The third if-statement body is not fully evaluated. The string is not a StringBuilder type.

using System; using System.Text; // Create a string variable and cast it to an object. string value1 = "Example"; object value2 = value1; // Apply the is-operator with 3 different parameters. if (value2 is object) { Console.WriteLine("is object"); } if (value2 is string) { Console.WriteLine("is string"); } if (value2 is StringBuilder) { Console.WriteLine("is StringBuilder"); // Not reached. }

is object is string

Is, pattern matching. Here we see a separate syntax form for the "is" operator. We have an object, and we want to cast it to a string. We use pattern matching for this.

Here The is-cast tests to see if the variable "wrapper" is a string. If it is a string, a string local called temp2 is introduced.

Important This use of the is-cast combines the as-cast with the is-cast. This is probably the best way to cast C# variables.

string temp = "ancient ship"; object wrapper = temp; // Use pattern matching to cast the object to a variable. // ... Wrapper is an object. // ... Temp2 is a string reference. if (wrapper is string temp2) { System.Console.WriteLine($"STRING = {temp2}, LENGTH = {temp2.Length}"); }

STRING = ancient ship, LENGTH = 12

Is, list matching. In newer versions of C#, we can use the is-keyword to perform pattern matching. So we can test the entire contents of a List with an is-statement.

Tip This is not casting, but is instead checking the entire contents of a List. It uses the same "is" operator.

using System; using System.Collections.Generic; List<int> values = [100, 200, 900]; // The is-keyword matches this list. if (values is [100, 200, 900]) { Console.WriteLine("SAME LIST"); } // This check evaluates to false. if (values is [-100, -1000]) { Console.WriteLine("???"); }

SAME LIST

Summary. The is-operator is exception-neutral. It is elegantly used in an if-statement expression—it is evaluated to a boolean value. We examined the instruction-level code.