Towards a more powerful and simpler C++ with Herb Sutter
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Towards a more powerful and simpler C++ with Herb Sutter
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Re: Towards a more powerful and simpler C++ with Herb Sutter
#2Are they really going to add $ to C++? Unbelievable. What was wrong with "reflexpr"? It is way more C++'ish than "$".
Update: From Herb's blog :
"Also, a vocal minority in the committee strongly want a syntax that does not include the $ character (not just for $class, but also for $expr reflection) because they have large code bases that use $ in source code that is not C++ code but is processed to emit C++; removing $ is an easy change at any time and we’ll just follow what the committee decides for reflection syntax (in fact, the alternative syntax I showed in the endnote above removes the need to write $). So further work is needed on those items, but fortunately none of it affects the core model."
https://herbsutter.com/2017/07/26/metaclasses-thoughts-on-ge...
P.S. I really hope that vocal minory would win ;)
But overall the proposal is what I have been talking about for a long time.
Re: Towards a more powerful and simpler C++ with Herb Sutter
#3Are they really going to add $ to C++? Unbelievable. What was wrong with "reflexpr"? It is way more C++'ish than "$". Update: From Herb's blog : "Also, a vocal minority in the committee strongly want a syntax that does not include the $ character (not just for $class, but also for $expr reflection) because they have large code bases that use $ in source code that is not C++ code but is processed to emit C++; removing…
The best way to add new language primitives without breaking anyone is to pick a syntax that currently fails to compile.
`reflexpr interface {...}` could be declaring and initializing a global.
`$class`, on the other hand, doesn't compile. One could also do `virtual class` or something, I guess, since `virtual class` is a combination of reserved keywords.
Re: Towards a more powerful and simpler C++ with Herb Sutter
#4Are they really going to add $ to C++? Unbelievable. What was wrong with "reflexpr"? It is way more C++'ish than "$". Update: From Herb's blog : "Also, a vocal minority in the committee strongly want a syntax that does not include the $ character (not just for $class, but also for $expr reflection) because they have large code bases that use $ in source code that is not C++ code but is processed to emit C++; removing…
The best way to add new language primitives without breaking anyone is to pick a syntax that currently fails to compile. `reflexpr interface {...}` could be declaring and initializing a global. `$class`, on the other hand, doesn't compile. One could also do `virtual class` or something, I guess, since `virtual class` is a combination of reserved keywords.
You are correct. But there is another side too. $ makes the language way uglier than it is now, and C++ is ugly language already.
Re: Towards a more powerful and simpler C++ with Herb Sutter
#5Are they really going to add $ to C++? Unbelievable. What was wrong with "reflexpr"? It is way more C++'ish than "$". Update: From Herb's blog : "Also, a vocal minority in the committee strongly want a syntax that does not include the $ character (not just for $class, but also for $expr reflection) because they have large code bases that use $ in source code that is not C++ code but is processed to emit C++; removing…
Its so much simpler :)
Re: Towards a more powerful and simpler C++ with Herb Sutter
#6Are they really going to add $ to C++? Unbelievable. What was wrong with "reflexpr"? It is way more C++'ish than "$". Update: From Herb's blog : "Also, a vocal minority in the committee strongly want a syntax that does not include the $ character (not just for $class, but also for $expr reflection) because they have large code bases that use $ in source code that is not C++ code but is processed to emit C++; removing…
Its so much simpler :)
I agree, but $ doesn't make the language way more uglier than what it is now?
Re: Towards a more powerful and simpler C++ with Herb Sutter
#7The interview covers proposed metaprogramming features in upcoming versions of C++. In particular, it demonstrates metaclass as a way for users to define new kinds of types, instead of relying solely on class/struct/union/enum.
For example, Java has an interface, in which methods are declared but not defined. The proposal for metaclass gives a demonstration of what an interface in C++ could look like:
interface Shape {
int area() const;
void scale_by(double factor);
};
// the dollar sign ($) prefix indicates reflection and metaprogramming
$class interface {
// the constexpr indicates compile-time execution
constexpr {
// raise an error if there are data members
compiler.require($interface.variables().empty(),
"interfaces may not contain data");
// loop over all functions
for (auto f : $interface.functions()) {
// raise an error if move/copy functions are present
compiler.require(!f.is_copy() && !f.is_move(),
"interfaces may not copy or move");
// function must be public
if (!f.has_access())
f.make_public();
compiler.require(f.is_public(),
"interface functions must be public");
// function must be virtual
f.make_pure_virtual();
}
}
// add a destructor
virtual ~interface() noexcept { }
};
See the full proposal here:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p070...
Re: Towards a more powerful and simpler C++ with Herb Sutter
#8Are they really going to add $ to C++? Unbelievable. What was wrong with "reflexpr"? It is way more C++'ish than "$". Update: From Herb's blog : "Also, a vocal minority in the committee strongly want a syntax that does not include the $ character (not just for $class, but also for $expr reflection) because they have large code bases that use $ in source code that is not C++ code but is processed to emit C++; removing…
I think the negatives (ugliness) of having $ in a few places where you define metaclasses is outweighed by the positives (cleanliness) of replacing this:
class foo {
virtual ~foo() = 0;
virtual void do_x() = 0;
};
interface foo {
void do_x();
};
Re: Towards a more powerful and simpler C++ with Herb Sutter
#9Are they really going to add $ to C++? Unbelievable. What was wrong with "reflexpr"? It is way more C++'ish than "$". Update: From Herb's blog : "Also, a vocal minority in the committee strongly want a syntax that does not include the $ character (not just for $class, but also for $expr reflection) because they have large code bases that use $ in source code that is not C++ code but is processed to emit C++; removing…
Next proposal will be about the new C++ logo, which will be, yes, a camel!
Re: Towards a more powerful and simpler C++ with Herb Sutter
#10Are they really going to add $ to C++? Unbelievable. What was wrong with "reflexpr"? It is way more C++'ish than "$". Update: From Herb's blog : "Also, a vocal minority in the committee strongly want a syntax that does not include the $ character (not just for $class, but also for $expr reflection) because they have large code bases that use $ in source code that is not C++ code but is processed to emit C++; removing…
It's still up in the air I think - you can see from his blog[1] that others in the the committee prefer a syntax more like
meta::type interface(const meta::type source) {
// … basically same code …
};