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In computer programming, specifically when using the imperative programming paradigm, an assertion is a predicate (a Boolean-valued function over the state space, usually expressed as a logical proposition using the variables of a program) connected to a point in the program, that always should evaluate to true at that point in code execution.
The following example written in Eiffel sets the value of a class attribute hour based on a caller-provided argument a_hour.The postcondition follows the keyword ensure.In this example, the postcondition guarantees, in cases in which the precondition holds (i.e., when a_hour represents a valid hour of the day), that after the execution of set_hour, the class attribute hour will have the same ...
[9] [29] Some assert that source code should be written with few comments, on the basis that the source code should be self-explanatory or self-documenting. [9] Others suggest code should be extensively commented (it is not uncommon for over 50% of the non-whitespace characters in source code to be contained within comments). [30] [31]
Example 1: legacy code may have been designed for ASCII input but now the input is UTF-8. Example 2: legacy code may have been compiled and tested on 32-bit architectures, but when compiled on 64-bit architectures, new arithmetic problems may occur (e.g., invalid signedness tests, invalid type casts, etc.). Example 3: legacy code may have been ...
The routine in the following example written in Eiffel takes as an argument an integer which must be a valid value for an hour of the day, i. e., 0 through 23, inclusively. The precondition follows the keyword require. It specifies that the argument must be greater than or equal to zero and less than or equal to 23.
In many programming languages, contracts are implemented with assert. Asserts are by default compiled away in release mode in C/C++, and similarly deactivated in C# [8] and Java. Launching the Python interpreter with "-O" (for "optimize") as an argument will likewise cause the Python code generator to not emit any bytecode for asserts. [9]
The program is then monitored for exceptions such as crashes, failing built-in code assertions, or potential memory leaks. Typically, fuzzers are used to test programs that take structured inputs. This structure is specified, such as in a file format or protocol and distinguishes valid from invalid input.
Common programming languages like Python, [3] PHP, [4] JavaScript, [citation needed] C++ and Java support assertions by default, which can be used to define class invariants. A common pattern to implement invariants in classes is for the constructor of the class to throw an exception if the invariant is not satisfied.