singleton variable


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singleton variable

(programming)
A variable which is only referred to once in a piece of code, probably because of a programming mistake. To be useful, a variable must be set and read from, in that order. If it is only referred to once then it cannot be both set and read.

There are various exceptions. C-like assignment operators, e.g. "x += y", read and set x and return its new value (they are abbreviations for "x = x+y", etc). A function argument may be passed only for the sake of uniformity or to support future enhancements. A good compiler or a syntax checker like lint should report singleton variables but also allow specific instances to be marked as deliberate by the programmer.
References in periodicals archive ?
There were 3 singleton variable sites (at position 177, 198, 222) and 7 Parsimony informative sites at position 64, 135, 143, 174, 187, 197, 199.
An excess of singleton variable sites may be an evidence for population expansion (William et al.
014 (ns) -- n = Number of samples; P = Parsimony informative sites; S = Singleton variable sites; #h = Number of haplotypes.
63% of all sites), of which 31 sites were singleton variable sites and one site was parsimony informative polymorphic site.