fmtindex

Fmtindex is a term used in text formatting and templating systems to denote a numeric index into an ordered list of values that will be substituted into a format string. It is most commonly found in libraries that support positional or reordered arguments, rather than relying on the position of values in the input data.

Semantics: A placeholder in a format string may include a fmtindex to indicate which argument to insert. For example, in languages with zero-based indexing, a placeholder like {0} refers to the first argument; {1} to the second. Some systems support both zero-based and one-based indexing, and some allow reusing the same fmtindex multiple times.

Implementation: During formatting, the engine scans the string, extracts fmtindex tokens, and retrieves the corresponding value from the supplied argument list. If the index is out of range, formatting typically raises an error or handles it with a fallback.

Variants: fmtindex is related to, but distinct from, named arguments (where placeholders reference by name) and automatic field numbering. In some templating languages, the term may be synonymous with positional placeholders, while others expose it as a separate concept.

Usage considerations: When accepting user-provided format strings, explicit fmtindex handling enables flexible reordering but also increases risk of errors or vulnerabilities if not properly validated. Clear documentation and defensive parsing are advised.

See also: Format string, Positional argument, Named argument, String interpolation, Placeholder.