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"Null" （编译类型）

"Null"

represents a type to indicate the absence of a result.

更多信息

  • "Null" can be used in Typed and related constructs to specify a type.
  • Terminating code with a semicolon such as expr; is a typical way to return "Null" from a function.
  • Functions that return "Null" do not return anything useful but typically change the state of a program.

Properties

  • The only value held by "Null" comes from compilation of the symbol expression Null.

Conversions

    From Expressions

  • The Null expression can be converted into compiled code elements with the type "Null".

    • To Expressions

  • "Null" compiled elements can be converted into Null expressions.

范例

基本范例  (2)

"Null" can be used as an output from a CompiledCodeFunction:

Call the function that prints a string and returns a "Null" result:

The Null symbol can be seen with InputForm:

A function that assigns to a raw pointer can return Null to indicate that it is changing the state of an argument:

The return type is "Null":

Generate a raw pointer to an integer:

Call the compiled function with the unmanaged value; it returns Null:

The integer stored in the raw pointer has been set: