Built-in types (C# reference)

The following table lists the C# built-in value types:

The following table lists the C# built-in reference types:

In the preceding tables, most C# type keywords from the left column are aliases for the corresponding .NET type. They're interchangeable. For example, the following declarations declare variables of the same type:

int a = 123;
System.Int32 b = 123;

The dynamic type is similar to object. The main differences are:

• Operations on a dynamic expression are bound at runtime, not at compile time.
• You can't use new dynamic().
• You can't derive a type from the dynamic type.

The delegate keyword is a built-in reference type keyword that declares a type derived from System.Delegate. Unlike the other built-in type keywords, delegate isn't an alias for a specific .NET type. Instead, it declares custom types that derive from the abstract System.Delegate type. Similarly, dynamic represents runtime binding behavior rather than being a direct alias for a specific .NET type.

The void keyword represents the absence of a type. You use it as the return type of a method that doesn't return a value.

The C# language includes specialized rules for the System.Span<T> and System.ReadOnlySpan<T> types. These types aren't classified as built-in types, because there aren't C# keywords that correspond to these types. The C# language defines implicit conversions from array types and the string type to Span<T> and ReadOnlySpan<T>. These conversions integrate Span types into more natural programming scenarios. The following conversions are defined as implicit span conversions:

• From any single-dimensional array with element type E to System.Span<E>
• From any single-dimensional array with element type E to System.ReadOnlySpan<U>, when E has covariance conversion or an identity conversion to U
• From System.Span<E> to System.ReadOnlySpan<U>, when E has a covariance conversion or an identity conversion to U
• From System.ReadOnlySpan<E> to System.ReadOnlySpan<U>, when E has a covariance conversion or an identity conversion to U
• From string to System.ReadOnlySpan<char>

The compiler never ignores any user defined conversion where an applicable implicit span conversion exists. Implicit span conversions can be applied to the first argument of extension methods, the parameter with the this modifier. Implicit span conversions aren't considered for method group conversions.

See also

• Use language keywords instead of framework type names (style rule IDE0049)
• Default values of C# types