One technique to ensure references are never set to null is to ensure every local variable of a reference type is initialized when it is declared. This is often referred to as non-null by construction. That previously wasn't easy for variables you intend to initialize by passing them to methods as out parameters. Starting with C# 7.0, you can declare out variables in the argument list of a method call, rather than writing a separate declaration statement. Try the following code:
You can change the int declaration to a var declaration. Change the declaration to the following code:
if (int.TryParse(input, out var result))The new syntax provides two important advantages over the existing syntax:
- The code is easier to read.
- You declare the out variable where you use it, not on another line above.
- No need to assign an initial value.
- By declaring the
outvariable where it is used in a method call, you can't accidentally use it before it is correctly assigned.
- By declaring the
The declared variable's scope is the scope enclosing the if statement. This allows you to use the variable afterwards. Modify the last if block as shown in the following snippet.
In C# 7.1, out variable declarations have been extended to include field initializers, property initializers, constructor initializers, and query clauses. It enables code such as the following example: