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built-in-typescsharp/language-reference/builtin-types

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Built-in types (C# reference)

Learn C# built-in value and reference types

  • page csharp/language-reference/builtin-types/built-in-types
  • updated 01/14/2026

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

C# type keyword .NET type
bool System.Boolean
byte System.Byte
sbyte System.SByte
char System.Char
decimal System.Decimal
double System.Double
float System.Single
int System.Int32
uint System.UInt32
nint System.IntPtr
nuint System.UIntPtr
long System.Int64
ulong System.UInt64
short System.Int16
ushort System.UInt16

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

C# type keyword .NET type
object System.Object
string System.String
delegate System.Delegate
dynamic System.Object

ms.custom: "updateeachrelease"

The C# language reference documents the most recently released version of the C# language. It also contains initial documentation for features in public previews for the upcoming language release.

The documentation identifies any feature first introduced in the last three versions of the language or in current public previews.

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:

csharp
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 and System.ReadOnlySpan 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 receiver parameter of extension members. The receiver parameter is specified by the extension keyword in an extension member. The receiver parameter is the first parameter of an extension method using the this modifier. Implicit span conversions aren't considered for method group conversions.

See also