Markus, 'hello' is a literal string constant, part of the set of constants of a method (or a doit which like a temporary method disconnected from a class).
Constants like these are managed by the compiler and can be shared between different expressions to avoid duplication. Changing such a constant is dangerous because it means you are changing static/compiled code. Consider a method like name ^ 'Markus' I could call this method and change the returned string destructively in place. Next time someone calls it, s/he would get the modified string. Even worse, s/he would not understand since the source code did not change. In the past it was not possible to mark such strings as being constant, now we can. Which is a big win. You can use #copy to get a string that you can modify. 'hello' copy at: 2 put: $a; yourself HTH, Sven > On 28 Feb 2021, at 00:50, Markus Wedel <m...@markus-wedel.de> wrote: > > Hi all, > > strings in Playground are read only in Pharo 9.0 Build 1153 so that > > 'hello' at: 2 put: $a; yourself > ctrl+p > > This throws an error: > „Modification forbidden: ‚hello‘ is read-only, hence its field cannot be > modified with $a > > which is actually a very nice error message but is this supposed to happen? > The example does work in Pharo 8 without problems. > > > Greetings > Markus
