A String Editing Class

by Finnian Reilly (modified: 2018 Oct 15)

    Contents
  1. Introducing Class EL_STRING_EDITOR
    1. Descendants
  2. An Example
    1. Without using EL_STRING_EDITOR
    2. Using EL_STRING_EDITOR

Introducing Class EL_STRING_EDITOR

I have added a new class EL_STRING_EDITOR to Eiffel-Loop that is very useful when you want to edit the contents of a string between all occurrences of a pair of delimiters.

A typical application is editing the text between markup tags. The beauty of this class is an agent routine allows you edit all delimited sections as an isolated string. The routine for_each takes care of incorporating the edits into the target string.

It has been added to github but is not yet part of any release.

Descendants

  EL_STRING_EDITOR*
     EL_ZSTRING_EDITOR
     EL_STRING_8_EDITOR
     EL_STRING_32_EDITOR

For convenience a new routine edit has been add to class EL_ZSTRING that applies the editor to Current.

edit (left_delimiter, right_delimiter: READABLE_STRING_GENERAL; a_edit: PROCEDURE [INTEGER, INTEGER, ZSTRING]) local editor: EL_ZSTRING_EDITOR do create editor.make (Current) editor.for_each (left_delimiter, right_delimiter, a_edit)

An Example

Here is a "before and after" example that demonstrates expansion of Wiki-markup with and without using class EL_ZSTRING_EDITOR. See routine substitute_html.

Without using EL_STRING_EDITOR

Getting the indices right is quite tricky as editing the text changes the offsets. class MARKUP_SUBSTITUTION inherit EL_STRING_CONSTANTS create make, make_hyperlink feature {NONE} -- Initialization make (a_delimiter_start, a_delimiter_end, a_markup_open, a_markup_close: ZSTRING) do delimiter_start := a_delimiter_start; delimiter_end := a_delimiter_end markup_open := a_markup_open; markup_close := a_markup_close end make_hyperlink (a_delimiter_start: ZSTRING) do make (a_delimiter_start, Right_square_bracket, Empty_string, Empty_string) is_hyperlink := True end feature -- Status query is_hyperlink: BOOLEAN feature -- Basic operations substitute_html (html: ZSTRING; new_expanded_link: FUNCTION [ZSTRING, ZSTRING, ZSTRING]) local pos_open, pos_close, pos_space: INTEGER; done: BOOLEAN expanded_link, link_path, link_text: ZSTRING do from until done loop pos_open := html.substring_index (delimiter_start, pos_open + 1) if pos_open > 0 then pos_close := html.substring_index (delimiter_end, pos_open + delimiter_start.count) if pos_close > 0 then if is_hyperlink then pos_space := index_of_white_space (html, pos_open + delimiter_start.count, pos_close - 1) if pos_space > 0 and then pos_space < pos_close then link_path := html.substring (pos_open + 1, pos_space - 1) link_text := html.substring (pos_space + 1, pos_close - 1) else link_path := html.substring (pos_open + 1, pos_close - 1) link_text := link_path end expanded_link := new_expanded_link (link_path, link_text) html.replace_substring (expanded_link, pos_open, pos_close) pos_open := html.index_of ('>', pos_open) else html.replace_substring (markup_open, pos_open, pos_open + delimiter_start.count - 1) pos_close := pos_close + markup_open.count - delimiter_start.count html.replace_substring (markup_close, pos_close, pos_close + delimiter_end.count - 1) end end end done := pos_open = 0 or pos_close = 0 end end feature -- Access delimiter_end: ZSTRING delimiter_start: ZSTRING markup_close: ZSTRING markup_open: ZSTRING feature {NONE} -- Implementation index_of_white_space (html: ZSTRING; start_index, end_index: INTEGER): INTEGER -- index of white space character just before text -- (allowing links to be spread across 2 lines) local i: INTEGER do from i := start_index until Result > 0 or i > end_index loop if html.is_space_item (i) then Result := i end i := i + 1 end if Result > 0 then from Result := 0 until Result > 0 or i > end_index loop if not html.is_space_item (i) then Result := i - 1 end i := i + 1 end end end feature {NONE} -- Constants Right_square_bracket: ZSTRING once Result := "]" end end

Using EL_STRING_EDITOR

Note there is no longer any use for routine index_of_white_space which managed the case of a hyperlink being split across lines. Routine to_canonically_spaced gets rid of any tabs and new lines.

The code is much simpler because you now only have to think of indices that are relative to the the delimited substring rather then the full target string. The start_index and end_index of the delimited section has already been calculated for you. class MARKUP_SUBSTITUTION inherit EL_STRING_CONSTANTS create make, make_hyperlink feature {NONE} -- Initialization make (a_delimiter_start, a_delimiter_end, a_markup_open, a_markup_close: ZSTRING) do delimiter_start := a_delimiter_start; delimiter_end := a_delimiter_end markup_open := a_markup_open; markup_close := a_markup_close new_expanded_link := agent empty_link end make_hyperlink (a_delimiter_start: ZSTRING) do make (a_delimiter_start, Right_square_bracket, Empty_string, Empty_string) is_hyperlink := True end feature -- Status query is_hyperlink: BOOLEAN feature -- Basic operations substitute_html (html: ZSTRING; new_link_agent: like new_expanded_link) do if is_hyperlink then new_expanded_link := new_link_agent html.edit (delimiter_start, delimiter_end, agent expand_hyperlink_markup) else html.edit (delimiter_start, delimiter_end, agent expand_markup) end end feature -- Access delimiter_end: ZSTRING delimiter_start: ZSTRING markup_close: ZSTRING markup_open: ZSTRING feature {NONE} -- Implementation expand_markup (start_index, end_index: INTEGER; substring: ZSTRING) do substring.replace_substring (markup_close, end_index + 1, substring.count) substring.replace_substring (markup_open, 1, start_index - 1) end expand_hyperlink_markup (start_index, end_index: INTEGER; substring: ZSTRING) local expanded_link, link_path, link_text: ZSTRING space_index: INTEGER do substring.to_canonically_spaced space_index := substring.index_of (' ', 1) if space_index > 0 then link_path := substring.substring (2, space_index - 1) link_text := substring.substring (space_index + 1, substring.count - 1) else link_path := substring.substring (2, substring.count - 1) link_text := link_path end substring.share (new_expanded_link (link_path, link_text)) end empty_link (path, text: ZSTRING): ZSTRING do create Result.make_empty end new_expanded_link: FUNCTION [ZSTRING, ZSTRING, ZSTRING] feature {NONE} -- Constants Right_square_bracket: ZSTRING once Result := "]" end end