How to escape control characters?

[Salih Dincer]

On Tuesday, 23 August 2022 at 23:17:21 UTC, Salih Dincer wrote:
>
> The nice thing here is that you can change the format 
> specifiers as you wish.

Actually, both structures could be combined:

```d
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 at 79