On Thursday, 31 March 2016 at 03:15:49 UTC, cy wrote:

The easiest is this:

import std.conv;
string str = `Hello "World"
line 2`;
writeln([str].text[2..$-2]); // Hello \"World\"\nline 2

I know this is an old post, but I felt this trick needed to be shared.

This takes advantage of the fact that std.format escapes the characters in an array of strings. So we create an array where str is the only element, and convert that to text. Without the [2..$-2] slicing the output would be ["Hello \"World\"\nline 2"].

A slightly more efficient implementation is

string escape(string s)
{
    import std.array : appender;
    import std.format : FormatSpec, formatValue;

    FormatSpec!char f;
    auto w = appender!string;
    w.reserve(s.length);
    formatValue(w, [s], f);
    return w[][2 .. $ - 2];
}

And the inverse:

string unescape(string s)
{
    import std.format : FormatSpec, unformatValue;

    FormatSpec!char f;
    string str = `["` ~ s ~ `"]`;
    return unformatValue!(string[])(str, f)[0];
}

Perhaps escape() and unescape() should be part of std.format so that they can be refactored to use std.format.internal.write.formatElement directly, eliminating the conversion to array.

-- Bastiaan.

On 8/23/22 6:09 AM, Bastiaan Veelo wrote:

import std.conv;
string str = `Hello "World"
line 2`;
writeln([str].text[2..$-2]); // Hello \"World\"\nline 2

string escape(string s)
{
     import std.array : appender;
     import std.format : FormatSpec, formatValue;

     FormatSpec!char f;
     auto w = appender!string;
     w.reserve(s.length);
     formatValue(w, [s], f);
     return w[][2 .. $ - 2];
}

Without allocations. This took me longer than I had hoped it would. It needs the 1-char buffer to avoid sending the surrounding quotes.

struct EscapedString
{
   string[1] str;
   this(string str) @nogc pure nothrow @safe { this.str[0] = str; }
   void toString(Out)(auto ref Out output)
   {
      import std.format;
      import std.range;
      char buf; // 0xff => empty, 0x0, empty, but not first
      void putter(const(char)[] data) {
         if(!data.length) return;
         if(buf != 0xff)
         {
            if(buf)
               put(output, buf);
         }
         else
            // skip first "
            data = data[1 .. $];
         if(!data.length){
            buf = 0;
            return;
         }
         put(output, data[0 .. $-1]);
         buf = data[$-1];
      }
      scope x = &putter;
      formattedWrite(x, "%(%s%)", str[]);
   }
}

It would be nice to expose the escaping functionality from format so this kind of trickery isn't necessary.

-Steve

On Tuesday, 23 August 2022 at 13:09:01 UTC, Steven Schveighoffer wrote:

Surely what Steve does is better. But for some reason I like simple and useful things.

I sometimes use custom string wrapping. Maybe it will be useful for you, for example:

struct String {
  string str;
  alias str this;
  import std.format, std.string;
  void toString(scope void delegate(const(char)[]) sink,
                FormatSpec!char fmt)const
  {
    auto arr = str.lineSplitter;
    if(fmt.spec == 'n') {
      sink.formattedWrite("%-(%s\\n%)", arr);
    } else sink.formattedWrite("%s", str);
  }
} unittest {
  import std.stdio;
  auto str = `this
  is a
  string`;
  String Str; // simple constructor
  Str = str; // direct assign

  Str.writefln!"%n"; // "this\n  is a\n  string"
  Str.writefln!"%s"; /*
this
  is a
  string
*/
}

The nice thing here is that you can change the format specifiers as you wish.

Thank you all...

SDB@79

On Tuesday, 23 August 2022 at 23:17:21 UTC, Salih Dincer wrote:

Actually, both structures could be combined:

struct EscapedString
{
   string[1] str;
   this(string str) @nogc pure nothrow @safe
   {
     this.str[0] = str;
   }

   import std.format, std.range;
   void toString(scope void delegate(const(char)[]) sink,
                 FormatSpec!char fmt)const
   {
     if(fmt.spec == 'e')
     {
       char buf;
       formattedWrite((const(char)[] data) {
         if(!data.length) return;

         if(buf < 0xff) put(sink, buf);
         else data = data[1 .. $];

         if(data.length) {
           put(sink, data[0 .. $-1]);
           buf = data[$-1];
         } else {
           buf = 0;
           return;
         }
       }, "%(%s%)", str[]);
     } else sink.formattedWrite("%s", str[0]);
   }
} unittest {
  import std.array : appender;
  import std.format;

  auto str = EscapedString();
  auto app = appender!string;

  app.formattedWrite("%e", str);
  assert(app.data.length == 0);

  auto results = [`a\tb`, `a\tba\nb`, `a\tba\nba\rb`,
                  `a\tba\nba\rba b`, `a\tba\nba\rba ba\"b`
                 ];

  foreach(i, char c; [9, 10, 13, 32, 34]) {
    const s = "a" ~ c ~ "b";
    app.formattedWrite("%e", EscapedString(s));
    assert(app.data == results[i],
           format("%s, i = %s", app.data, i));
  }
}

SDB@79