By contrast, changing the value of the deckSize variable in the second example would be a simple, one-line change. Second, it would likely replace the characters "52" everywhere, regardless of whether they refer to the deck size or to something else entirely, such as the number of weeks in a Gregorian calendar year, or more insidiously, are part of a number like "1523", all of which would introduce bugs. First, it would miss the value 53 on the second line of the example, which would cause the algorithm to fail in a subtle way. To modify the first example to shuffle a Tarot deck, which has 78 cards, a programmer might naively replace every instance of 52 in the program with 78. Also, when two semantically distinct variables or numbers have the same value they may be accidentally both edited together. Changing the value of a magic number is error-prone, because the same value is often used several times in different places within a program. It is easier to alter the value of the number, as it is not duplicated.Magic numbers become particularly confusing when the same number is used for different purposes in one section of code.
#Magic duels trial of knowledge code#
A programmer reading the first example might wonder, What does the number 52 mean here? Why 52? The programmer might infer the meaning after reading the code carefully, but it is not obvious. It is considered better programming style to write the following: In the preceding example, 52 is a magic number. Where a is an array object, the function randomInt(x) chooses a random integer between 1 and x, inclusive, and swapEntries(i, j) swaps the ith and jth entries in the array. Thus, declaring const string testUserName = "John" is better than several occurrences of the 'magic value' "John" in a test suite.įor example, if it is required to randomly shuffle the values in an array representing a standard pack of playing cards, this pseudocode does the job using the Fisher–Yates shuffle algorithm: The problems associated with magic 'numbers' described above are not limited to numerical types and the term is also applied to other data types where declaring a named constant would be more flexible and communicative. An example of an uninformatively-named constant is int SIXTEEN = 16, while int NUMBER_OF_BITS = 16 is more descriptive. Names chosen to be meaningful in the context of the program can result in code that is more easily understood by a maintainer who is not the original author (or even by the original author after a period of time). Replacing all significant magic numbers with named constants makes programs easier to read, understand and maintain. is every digit correct in 3.14159265358979323846 and is this equal to 3.14159?) and makes it more difficult for the program to be adapted and extended in the future. The use of unnamed magic numbers in code obscures the developers' intent in choosing that number, increases opportunities for subtle errors (e.g.
#Magic duels trial of knowledge manuals#
This has been referred to as breaking one of the oldest rules of programming, dating back to the COBOL, FORTRAN and PL/1 manuals of the 1960s. The term magic number or magic constant refers to the anti-pattern of using numbers directly in source code. In computer programming, the term magic number can refer to unique values with unexplained meaning or multiple occurrences which could (preferably) be replaced with named constants.
0 kommentar(er)
