What parent commenter meant was language level support of immutable objects. There is const, in for example JavaScript, but it supports only immutability of variables, not objects themselves. That later one is possible in C++ for example, where const can be used for both. Of course, it’s still possible to fake immutability with interfaces in some languages, or have a real one forced by implementation (like with Temporals), but it’s much nicer to have an indicator forcing that.
I would like to add, that both variable and object immutability should be the default, and mutability should have a keyword, not other way around how in C++ and Java.
What parent commenter meant was language level support of immutable objects. There is const, in for example JavaScript, but it supports only immutability of variables, not objects themselves. That later one is possible in C++ for example, where const can be used for both. Of course, it’s still possible to fake immutability with interfaces in some languages, or have a real one forced by implementation (like with Temporals), but it’s much nicer to have an indicator forcing that.
I would like to add, that both variable and object immutability should be the default, and mutability should have a keyword, not other way around how in C++ and Java.