TITLE

Data: sprintf() with overloaded objects

VERSION

  Maintainer: Ilya Zakharevich <ilya@math.ohio-state.edu>
  Date: 15 Sep 2000
  Mailing List: perl6-language-data@perl.org
  Number: 235
  Version: 1
  Status: Developing

ABSTRACT

This RFC proposes a support of sprintf() with overloaded objects;

DESCRIPTION

The problems:

too many different flavors to support, many of them equivalent;
Many different flags, a lot of work to implement them all.
* in the flags.

One would want an interface which allows to get acceptable results with a minimal of work, but also allows as fine control as possible if needed. The solution:

merge many flavors into groups, with one overloaded operation per group. For example, '%i' and '%d' should invoke the same overloaded operation keyed by %d (or %?d, see below).
provide the actual letter (and flags!) as an argument to disambiguate it inside the group;
provide two operations to overload per group (only one of them should be used), for example '%+040d' should invoke the operation keyed by '%?d' if present, otherwise one keyed by '%d', then would postprocess the results. Similarly, '%d' should invoke the operation keyed by '%d' if present, otherwise one keyed by '%d'.
If * is present in the flags, the count is provided as an additional argument to the corresponding method. (One additional argument per each *.)

For example, if method '%d' is overloaded by the method FORMAT_D, and '%?d' is not overloaded, then

  sprintf('%s %0*i %s', '--', $overloaded_object, 10, '--')

calls

  $overloaded_object->FORMAT_D('0*i', 10);

and postprocesses the result.

Composite objects

The "standard" semantic of processing flags in the overloaded methods for composite objects (such as complex numbers or vectors) should be: delegate the flags to components "as is". (As opposed to applying widths to the total field.)

There may be obvious exceptions: for complex numbers +/- before the imaginary part is needed, but if one inserts this sign no matter what, the format '%+10i' would result in a double + sign or +- or --. The other approach of prepending '+' to the flags no matter what would omit space for the format '% 10i'.

MIGRATION ISSUES

NONE

IMPLEMENTATION

More or less straightforward

REFERENCES

RFC ???

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