What is the C# Null Coalescing Operator (??)?

In -depth understanding of the powerful function of the C# air merger (??)

In C# programming, you may have encountered a mysterious code:

This line of code contains a set of striking dual question marks "??", which has caused people's curiosity. Are they a new form of a ternary computing symbol?

<code class="language-csharp">FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();</code>

Unveiled the empty merger operation symbol

The answer lies in the concept of air merger (??). Similar to Sanyuan (immediately if) operational character, the air merger operator provides a simple method to evaluate whether the value is empty.

Expand expression

Expand the above expression and get the following logic equivalent items:

further expand into a more familiar format:

<code class="language-csharp">FormsAuth = formsAuth != null ? formsAuth : new FormsAuthenticationWrapper();</code>

Meaning and usage

<code class="language-csharp">if (formsAuth != null)
    FormsAuth = formsAuth;
else
    FormsAuth = new FormsAuthenticationWrapper();</code>

In essence, if the value on the left is not empty, the value of the air merging operator is the value on the left. Otherwise, it is silent as the value on the right. In other words, "If the value on the left is not empty, use it; otherwise, use the value on the right."

This operator is particularly useful for using the default value initialization variables to ensure that they remain non -empty during program execution. It can also be used in order to use multiple air merger operators to ensure the first non -empty value assignment.

Details worth noting

Although the concept is equivalent to the expansion of the above, it must be noted that the air merger operator only evaluates each expression once. This is particularly important if one of the expressions involving the method of possible side effects.

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