String Interpolation

This is a small string interpolation library for Nim providing a prinftf-like syntax. The library was inspired by Scala's string interpolation and provides a similar interface.

Basically there are three formatting templates/macros:

• ifmt*(formatString: string): expr

  Internally, this is a wrapper for format. The format string can contain indentifiers ifmt"x = $x" or expressions ifmt"x = ${x+1}". Both can have a printf format suffix e.g. ifmt"iteration = $i%5d, error = ${error*100}%6.2f %%". If there are no formatters, a %s formatter will be used, which will lead to a call to $ (see format). In order to escape $ or % in the format string, use $$ and %%. A type mismatch or an ill-formated format string produces a compile-time error.

• format*(formatString: string{lit}, args: varargs[expr]): expr

  This is a wrapper for formatUnsafe and performs additional type checking of the arguments. There is a special rule for %s: If the correponding argument is not a string, the macro will issue a call to $ to convert it. If all arguments have proper type (or can be converted to string), a call to formatUnsafe is generated. Due to the compile-time type checking formatString must be a static string literal.

• formatUnsafe*(formatString: string, args: varargs[expr]): string

  This template provides a simple wrapper for snprintf. No type checking is performed, allowing to use dynamic format strings. Internally, the template takes a two-step approach: In a first call to snprintf a fixed size (256) buffer is provided. If snprintf reports that the buffer was too small, a second call is performed with exactly the size required. As a result, there is no limitation on the maximum string size of the arguments.

TODO:

• The validation of printf formatters is still very basic. Lots of room for improvement.
• Much more testing is required, especially regarding various type checks.