[alpatters]

The extra syntax is not there for nothing. It's adding type information. Thus allowing error checking or dispatching by type or optimisations at compile time. It is a cost in terms of syntax and readability but it's not for nothing.

So for correct programs the end result might be the same in terms of values. For buggy code and runtime speed that's not necessarily the case.

[jlarocco]

The extra code is there for a reason, but it's still there and it's not there in a language like Python.

Nobody would argue that C++11 code can be much cleaner than old C++ code. But to say it's almost as clean as Python goes to far, and isn't fooling anybody. So why not be satisfied beating old C++?

[danking00]

And this is where I decide the language is too far developed on the wrong foundation.

I cannot put up with type systems that don't have complete or near-complete type inference. I don't know why one would start a new project in a language that didn't support Hindley-Milner.

[Locke1689]

Just to elaborate on what danking00 is saying, the extra syntax in this case is not adding any extra information (to the compiler). The left hand type of the expression can be completely inferred at compile time, in this case. What that required syntax is adding is pain, but no gain (except for imperceptibly faster compile time).

In Haskell this would look like:

  TagDataMap = [
          ("title", ((3, 30, stripnulls)),
          ("artist", ((33, 30, stripnulls)),
          ...

Haskell will correctly infer that TagDataMap :: [(String, (Integer, Integer, String -> String)].

Ok, technically this is an associative list, not a Python dictionary, but it is a map and can be accessed like one. Hell, most people use dictionaries with less than 10 items, which are much slower than arrays most of the time

[fusiongyro]

"the extra syntax in this case is not adding any extra information (to the compiler)." This actually isn't true in C++, because there could be many classes in scope that could take a list initializer like this. In Haskell, no literal with [] can "turn into" something besides a list, but that can happen in C++:

    vector<int> items = {1,2,3,4};
    int[] items       = {1,2,3,4};

These have different types, so how would C++ know which one you meant if you instead wrote:

    auto items = {1,2,3,4};

Again, in Haskell this isn't a problem because literals have essentially a single type. (Edge cases around integers and strings notwithstanding).

Edit: Just to clarify, in a Hindley-Milner system you could maybe get away with something like that, but everything you name in an HM system you must use, and that isn't the case in C++:

    void foo() {
      auto items = {1,2,3,4};
      return;
    }

I can then make two classes with list constructors:

    struct FooClass {
      FooClass(std::initializer_list<int> list) {
        cout << "Made a Foo!" << endl;
      }
    };

    struct BarClass {
      BarClass(std::initializer_list<int> list) {
        format_your_hard_disk();
      }
    };

Obviously there are consequences to choosing the right type, but the type of that value never leaks out of the function. Nevertheless, because side-effects can happen anywhere, even in a constructor, C++ cannot optimize that out.

This might be a convoluted example, and it may be flawed, but conjuring up others is not hard and demonstrates that C++ simply cannot ever have true HM type inferencing. Since the "real deal" is not possible, the language is complex and the standard is large, I would not expect to be able to live without annotations in C++-land. (Again, the FQA makes the horror of multiple non-orthogonal solutions to the same problems quite clear).

[danking00]

Your example,

    void foo() {
      auto items = {1,2,3,4};
      return;
    }

is the case of poorly designed syntax, in a truly Hindley-Milner system there is no expression which doesn't have a type. Now, we could add some syntax that screws that up, say:

    let v = I-HAVE-AN-AMBIGUOUS-TYPE in 0

But that's rather silly, isn't it? If a value isn't used then I would, personally, like my language to optimize it away. So why not ditch such silly syntax?

This is part of why I said that the foundations of C++ are too far-gone.

And this syntax isn't necessary to save on typing. In a language that supported syntactic macros (such as Scheme or Racket) we could write something like:

   auto items = my-vector-syntax(1,2,3,4);

which expands to something like:

    auto items;
    items.push_back(1);
    items.push_back(2);
    items.push_back(3);
    items.push_back(4);

If you're interested in true syntactic macros for non-sexp languages (though I do suggest getting over the parentheses, my color settings make them nearly indistinguishable from the background) look at Rust [1].

Actually, Rust also has type inference [2].

Hell, stop programming in C++ and start using Rust! [3]

[1] http://dl.rust-lang.org/doc/tutorial-macros.html [2] http://dl.rust-lang.org/doc/0.4/rust.html#type-system [3] http://www.rust-lang.org/

[fusiongyro]

Having programmed Haskell for the last seven years (and C++ for zero) I have a fairly decent handle on what HM is all about. If all you had said is that the foundations of C++ are too far gone, there wouldn't be anything to discuss. But the foundations of C++ being what they are, there's no point being offended when unfixable things go unfixed. I love HM, but you can't just throw it in any old language simply because it's cool. The language's semantics need to allow for it, and they just don't with C++.

[danking00]

Correct, I do not suggest adding HM to C++.

I suggest using a HM language when you start a new project.

[comex]

It's possible to do exactly that (a function that initialized a vector with its arguments) in C++ with variadic templates...

You might end up in trouble if you did something like

    auto v = vec(
                  vec(1.2, 3.4),
                  vec(0)
                )

not sure how well other languages deal with that.

[daivd]

"Hell, stop programming in C++ and start using Rust!" I plan to try to do that, when Rust has become more stable.

[kibwen]

No need to downvote this; I'm an enthusiastic Rust follower and I as well recommend that you stay far away from Rust until it settles down a bit. Wait for 0.5 if you're adventurous, 0.6 if you expect some degree of feature-completion, 0.7 if you're fine with half-finished standard libraries, and even later if you expect a high degree of stability, ergonomics, documentation, or performance.

[Locke1689]

This is definitely true and demonstrates how competing design decisions can add huge complexity to a language. C++ made earlier design goals to allow heavily context-dependent overriding, which has side effects on what features it can add later.

[Peaker]

Integers and Strings aren't edge cases. Their literals are polymorphic and typed.

C++ could also type its list initializers with some polymorphic type (similar to Haskell's Num) but didn't do so.

This is not inherent.

[fusiongyro]

They're not worth discussing because they're a counterintuitive mess rather than a case study of the glory of HM. Maybe edge case isn't the right word, but they're definitely not something I would hail as a perfect resounding success.

There are no polymorphic literals in ML, just polymorphic math operators, which is enough of a blight on the standard that OCaml discarded it and forces you to use different operators for real and integer arithmetic. And there's only one kind of string in both MLs.

Haskell's Num hierarchy is troublesome. They traded usability for + with complexity for /. It's extremely unlikely that you could write a program in Haskell that does much arithmetic and have it build correctly on the first try without any manifest typing. This is one reason students of Haskell find things so confusing: type declarations are necessary at the top level simply because the extensions and complexity of modern Haskell break HM if you try using it everywhere. Also, the class system in there is not especially mathematically correct, which leads to the numerous replacement Preludes that try to do a better job but haven't caught on.

Strings are edge cases because they are not polymorphic unless you enable OverloadedStrings. Once you do, you will either replace the built-in string with something else (ByteString or Text) or find yourself in the same kind of trouble you'd be in with Num.

Let me be clear: I'm not saying that these problems are showstoppers. They're really minor annoyances once you're experienced, though they contribute to confusion for beginners. The point I'm trying to make is that you can't just drop HM into any old language and expect it to work. A greater point would perhaps be that all languages have warts simply because they're large, complex beasts (Haskell and C++ especially) and it's unproductive to point to a missing feature in one and demand some sort of perfected version of the other's.

[Peaker]

> They're not worth discussing because they're a counterintuitive mess

Do you really believe Num overloading is a counterintuitive mess? I disagree completely.

> OCaml discarded it and forces you to use different operators for real and integer arithmetic

Which is pretty terrible.

> Haskell's Num hierarchy is troublesome.

Yes, but that's an orthogonal issue.

> This is one reason students of Haskell find things so confusing: type declarations are necessary at the top level simply because the extensions and complexity of modern Haskell break HM if you try using it everywhere

That sounds like FUD to me, a heavy Haskell user. Type declarations at the top-level are generally necessary to avoid the dreaded MR and for documentation purposes. Modern Haskell doesn't heavily use extensions that require type annotations on the top-level.

> Strings are edge cases because they are not polymorphic unless you enable OverloadedStrings. Once you do, you will either replace the built-in string with something else (ByteString or Text) or find yourself in the same kind of trouble you'd be in with Num.

It lets me use literals for Lazy Text, Strict Text, and String with the same syntax, which is nice.

My point is merely that giving a type to a polymorphic initializer is possible, and C++ chose not to.

[daivd]

Even in Hindley-Miller type systems it is considered good practice to add types as documentation to top-level constructs (see Haskell). In Python it is also considered good practice to add argument and return type info in the doc string. In a dynamic language you would also have to add a unit test or two for cases for some of the things that the compiler can catch for you.

Looking at the complete picture makes a language with local type inference (like C++11) more or less as verbose as one with complete type inference.

[longlivedeath]

> it is considered good practice to add types as documentation to top-level constructs

But with type inference your tools can do that for you (e.g. C-u C-c C-t in haskell-mode).

[lmm]

A good IDE can fill in the types in C++ too.

[longlivedeath]

Is there a C++ IDE that can figure out the function signature after you have written something like

_ f(_ a, _ b, _ c) { YOUR; CODE; HERE; }

?

[codewright]

Wrong foundation? No. Foundation you don't want? Sure.

Try to remember that Hindley-Milner is very hard to do outside of functional languages like ML and Haskell.

[danking00]

Yes type inference is harder with C++'s language design (OO comes to mind as a particular problem), thus my claim that it's the wrong foundation to build on. Of course, people like challenging problems and are working to bring more type inference to OO languages [1].

Furthermore, I assert that this truly is the wrong foundation. For new projects that must have OO, Scala provides local type inference and object orientation. If you're really hurting for some manual memory management, look at Rust [3] or Habit [2].

If we can recover the features we love on a new foundation that provides new features like type inference or memory-safety, then we've found a better foundation, IMHO.

[1] http://www.cs.ucla.edu/~palsberg/typeflow.html

[2] http://hasp.cs.pdx.edu/habit-report-Nov2010.pdf

[3] http://www.rust-lang.org/

[Myrmornis]

This is what caught my eye too as being really ugly and hard to read.

  const map<const string, const tuple<int, int, StrToStr>> TagDataMap {
      {"title" , make_tuple( 3, 30, stripnulls)},

Why can't the compiler figure out the types involved in this map structure itself? The user-defined functions are declared above, make_tuple will be declared in some library, and the others are string/int literals.

[fusiongyro]

One thing you cannot do is infer `const`ness. This isn't a problem in Hindley-Milner systems because variables are not assignable--they're all `const`, all the time. Literals are inherently immutable but when you assign a C++ variable a literal value, sometimes you want a const variable and sometimes you don't.

I don't think C++ can figure out the map<..> part simply because lots of things could have list initializers that accept lists of 2 item lists. C++'s overloading and implicit conversion conflicts with perfect type inferencing. This is an example of the kind of thing the FQA talks about, where several of C++'s issues collide to produce counter-intuitive behavior.

I do wonder if you could get away with this:

    const map<const auto, const auto> TagDataMap { ...

I don't have access to a C++11 compiler from where I am to find out though. I am particularly unclear on the interaction between `auto` and other aspects of a type declaration--I don't know if you can nest `auto` like this deep inside some other type declaration. I don't see why you couldn't, but wouldn't be shocked either.

[bcoates]

You can't do it with that syntax. 'auto' never infers constructor calls, just takes the static type of an LHS to capture a temporary into. You'd have to use a non-constructor template function that inspects the type of its argument to guess what kind of map you want.

  const auto TagDataMap = map_initializer( { "foo", { 1, 20, func }, ... } );

where map_initializer would be a template function that inspects the typedefs of its std::initializer_list<T> argument and generates an appropriate map.

In real C++ code, this would almost never be what you actually want, though, as the types in an initializer list in C++ do not imply the types being initialized, they are parameters to a constructor to be determined elsewhere.

[fusiongyro]

Thanks for clearing that up. I'm just starting to play with C++11 and have some trouble getting to a supporting compiler from work.

[Evbn]

It would help a lot if the keyword 'const' were replaced by a punctuation character or shorter simpler keyword like 'val'

[hnriot]

that's not entirely true, take make_tuple for example, this doesn't add anything except verbosity (by comparison to Python)

[derleth]

> The extra syntax is not there for nothing.

You could say the same thing about everything old C++ compelled you to type. Or old COBOL, for that matter.

I'm more interested in what the C++ memory allocation style does to verbosity. Memory-handling styles are often more important than the traditional paradigms (functional, OO, etc.) in determining what's reasonable/pleasant to do in a given language.

https://sites.google.com/site/steveyegge2/allocation-styles

[eru]

But aren't all allocation styles basically the same once you get GC? (I guess unless you broaden the scope of the word, and let it describe the lengths you go in Haskell to avoid allocation at all, aka triggering stream fusion and automatic deforrestation in general.)

[Evbn]

There are other issues: Go has stuff like slice for efficiently allocating array data more finely than a Java array, perl has autovivication.

[drivebyacct2]

Yeah, I agree with the claim that this is not in the same realm of readability (seriously, just consider for 10 seconds what an at-scale C++11 codebase looks like versus a scaled up python code base. But I understand why they're different and I can't get enough of the statically typed kool-aid lately.

[Evbn]

I am picturing Python drowning in isinstance checks to avoid constant crashing every time a new function is added.

[drivebyacct2]

I'm just imagining how many nights in a row I've committed more lines of code than exist in my project in a snapshot because it's so damn confusing, interconnected, and concurrent. The thought of doing it in a dynamic language is downright nauseating.