Sigil (computer programming)
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In computer programming, a sigil is a symbol attached to a variable name, showing the variable's datatype. The term was first applied to Perl usage by Philip Gwyn in 1999 to replace the more cumbersome "funny character in front of a variable name". The name is presumably based on the word meaning a magical symbol (see sigil (magic)).
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[edit] Historical context
The use of sigils was popularized by the BASIC programming language. The best known example of a sigil in BASIC is the dollar sign (“$”) appended to the names of all strings. Many BASIC dialects use other sigils to denote integers and floating point numbers, and sometimes other types as well.
Larry Wall adopted shell scripting’s use of sigils for his popular scripting language Perl. However, as Perl is a weakly typed language, the sigils specify not fine-grained data types like strings and integers, but general categories such as scalars (using a prepended “$”), arrays (using a “@”), hashes (using a “%”), and subroutines (using a “&”). Perl 6 introduces secondary sigils, or twigils, which are used to indicate the scope of variables. Prominent examples of twigils in Perl 6 include “^”, used with self-declared formal parameters (“placeholder variables”), and “.”, used with object attribute accessors (i.e., instance variables).
[edit] Language comparison
In the PHP language, which was derived partly from Perl, “$” precedes any variable name. Names not prepended by this are considered constants.
In Ruby, ordinary variables lack sigils, but “$” is prefixed to global variables, “@” is prefixed to instance variables, and “@@” is prefixed to class variables (the second “@” cannot be considered a twigil, so “@@” is just a longer sigil).
[edit] Hungarian notation
Related to sigils is Hungarian notation, a convention for variable naming that specifies variable type by attaching certain alphabetic prefixes to the variable name. Unlike sigils, however, Hungarian notation provides no information to the compiler; as such, explicit types must be redundantly given for the variables and the prefixes are not enforced, making them more prone to omission and misuse.
