First class property

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A first-class citizen ( English first-class object , German about "Object First Class") refers to the programming of computer systems an object as arguments or return value of a function or procedure occurs or a variable can be assigned.

The term was coined by Christopher Strachey in the context of functions as first-class citizens in the mid-1960s.


An object is first class if it meets the following conditions:

  • it can be saved in program variables,
  • it can be passed as a parameter to functions or procedures,
  • it can serve as a return value of functions,
  • it can be created while a program is running and
  • it has its own identity (regardless of name).

The term object does not have to be understood in the narrower sense as an object of an object-oriented programming language . In most programming languages, the objects of the elementary data types , e.g. B. Integer and floating point objects, always first class.



  1. ^ Michael Scott: Programming Language Pragmatics . Morgan Kaufmann Publishers, San Francisco, CA 2006, p. 140.
  2. ^ Rod Burstall, "Christopher Strachey — Understanding Programming Languages," Higher-Order and Symbolic Computation 13 : 52 (2000)
  3. First Class . January 25, 2006. Retrieved October 9, 2010.
  4. ^ First class object . Retrieved October 9, 2010.