Immutable strings… in Delphi?

One of the “novelties” of the NextGen Delphi compiler is immutable strings, which I find quite puzzling, for lack of a better word, given that Delphi already had reference-counted copy-on-write strings, and the NextGen compiler uses reference-counted strings.

I always considered that Delphi’s String type was one of its remaining strong points, being a high-level abstraction (higher than Java’s or .Net’s String/StringBuilder dichotomy) with excellent low-level performance (on par with C/C++  character arrays).

From the recent discussions, it appears many don’t know what makes/made Delphi String so special, so here is a quick summary.