4 ms·

> Immutability is stronger than C++ const correctness and easier to use at the same time. C++-style const appears to be stronger than just immutability, since

> Immutability is stronger than C++ const correctness and easier to use at the same time. C++-style const appears to be stronger than just immutability, since you can have immutable objects in C++, but you can also pass const references to mutable objects.

barrkel 7y ago
Precisely why it's harder to use. C++ is more expressive, and thus creating self-consistent designs is harder.
- edflsafoiewq 7y ago
  You'll have to give me an example for that. Having static types is more expressive than not having static types, but I think types make designs easier to make and understand. const is just another layer to the type system.
  - barrkel 7y ago
    It's another aspect of type design you need to make decisions for. If you can't see that, I can't help you.
- pkolaczk 7y ago
  C++ is more expressive than what? Than C probably. Than Java/C# - arguable. Than Scala/Haskell/Rust/Python/Ruby/R - no way.
  - jcelerier 7y ago
    in which of these languages can you have types depending on values ? :=)
    - pkolaczk 7y ago
      In Scala and Idris. Haskell has no direct support, but I believe you can get quite close with rank-2 types. Also, typing is not the end of all the things. Most languages I listed have much stronger metaprogramming capabilities than C++. Scala, Rust, Template Haskell macro systems are superior to C++ templates.
  - barrkel 7y ago
    More expressive than Java, sure. Java doesn't have overloaded operators, or cv-qualifiers, or templates, or many many many other things that make the type design space more expressive. Ruby is hardly expressive at all in this respect - you can express to the interpreter very little about types, and the interpreter won't help you much at all.
    - pkolaczk 7y ago
      C++ doesn't have GC, reflection, annotations, code generation utilities (annotation processors, cglib, etc), first-class generic types, existential types, rich standard library etc. That's why it is "arguable". > you can express to the interpreter very little about types Dynamic types are still types. Only the error detection moment is different, but lack of static types doesn't mean low expressivity.
blackflame7000 7y ago
That's because it is undefined behavior to cast a const object to a non-const object. Instead, you must tell the compiler via the mutable keyword or else it will make optimizations based on the assumption it can't change.
pkolaczk 7y ago
A const reference to a mutable object doesn't guarantee that the object won't change contrary to an immutable object. Hence const is weaker than immutable. You can have immutable objects in C++, but C++ offers almost nothing to make dealing with such objects fast and easy. Also the lack of GC makes designing persistent data structures an order of magnitude harder task than in most other languages.
- AstralStorm 7y ago
  That's only if you do not use a library and/or have no idea how shared_ptr is implemented.
  - pkolaczk 7y ago
    The standard library doesn't come with persistent collections included. Just the fact that they are not standard like in some other languages, causes fragmentation. As for shared_ptr, they are a good idea when you don't care about performance. And they don't solve cycles, which may appear in some structures (e.g. graphs).

barrkel 7y ago

Precisely why it's harder to use. C++ is more expressive, and thus creating self-consistent designs is harder.

edflsafoiewq 7y ago
You'll have to give me an example for that. Having static types is more expressive than not having static types, but I think types make designs easier to make and understand. const is just another layer to the type system.
- barrkel 7y ago
  It's another aspect of type design you need to make decisions for. If you can't see that, I can't help you.
pkolaczk 7y ago
C++ is more expressive than what? Than C probably. Than Java/C# - arguable. Than Scala/Haskell/Rust/Python/Ruby/R - no way.
- jcelerier 7y ago
  in which of these languages can you have types depending on values ? :=)
  - pkolaczk 7y ago
    In Scala and Idris. Haskell has no direct support, but I believe you can get quite close with rank-2 types. Also, typing is not the end of all the things. Most languages I listed have much stronger metaprogramming capabilities than C++. Scala, Rust, Template Haskell macro systems are superior to C++ templates.
- barrkel 7y ago
  More expressive than Java, sure. Java doesn't have overloaded operators, or cv-qualifiers, or templates, or many many many other things that make the type design space more expressive. Ruby is hardly expressive at all in this respect - you can express to the interpreter very little about types, and the interpreter won't help you much at all.
  - pkolaczk 7y ago
    C++ doesn't have GC, reflection, annotations, code generation utilities (annotation processors, cglib, etc), first-class generic types, existential types, rich standard library etc. That's why it is "arguable". > you can express to the interpreter very little about types Dynamic types are still types. Only the error detection moment is different, but lack of static types doesn't mean low expressivity.

blackflame7000 7y ago

That's because it is undefined behavior to cast a const object to a non-const object. Instead, you must tell the compiler via the mutable keyword or else it will make optimizations based on the assumption it can't change.

pkolaczk 7y ago

A const reference to a mutable object doesn't guarantee that the object won't change contrary to an immutable object. Hence const is weaker than immutable. You can have immutable objects in C++, but C++ offers almost nothing to make dealing with such objects fast and easy. Also the lack of GC makes designing persistent data structures an order of magnitude harder task than in most other languages.

AstralStorm 7y ago
That's only if you do not use a library and/or have no idea how shared_ptr is implemented.
- pkolaczk 7y ago
  The standard library doesn't come with persistent collections included. Just the fact that they are not standard like in some other languages, causes fragmentation. As for shared_ptr, they are a good idea when you don't care about performance. And they don't solve cycles, which may appear in some structures (e.g. graphs).