AMDG On 02/14/2018 10:29 PM, Zach Laine via Boost wrote:
On Wed, Feb 14, 2018 at 4:45 PM, Steven Watanabe via Boost < boost@lists.boost.org> wrote:
On 02/14/2018 03:11 PM, Zach Laine via Boost wrote:
On Tue, Feb 13, 2018 at 4:51 PM, Steven Watanabe via Boost < boost@lists.boost.org> wrote:
algorithm.hpp:
221: template <long long I, typename Expr> decltype(auto) get (Expr && expr, hana::llong<I> i); Does this need to be restricted to hana::llong, rather than, say, std::integral_constant?
It's the lack of nice syntax for integral_constant literals that made me choose this. I write get(expr, N_c) a lot, and I expect users to as well.
Supporting an IntegralConstant doesn't mean that you can't pass 0_c.
Is the change from std::integral_constant to IntegralConstant significant? That is, are you asking that I accept models of some concept, or just std::integral_constant?
I meant hana::IntegralConstant in the first place. std::integral_constant was just an example of another IntegralConstant, which hana::at can accept.
<snip>
expression_free_operators.hpp/expression_if_else.hpp:
- Why is this not part of expression.hpp?
For the same reason that expression_free_operators.hpp is not. Those three headers are separate pieces that you may want some or all of, so I kept them separate.
expression_if_else makes a certain amount of sense as being separate. Making expression_free_operators separate comes with a high risk of ODR problems in any code that has different behavior depending on whether a given operator is defined. It's extra strange because expression_free_operators.hpp only has half the operator overloads, with the other half being defined as members.
I've read this a few times and don't get it. Without including expression_free_operators.hpp, where might the other ODR-colliding operators come from? Do you mean if the user defines her own operators for expression<>, and then includes expression_free_operators.hpp in another TU, or something else?
I was talking about the one definition rule as applied to some function that uses the operators. As an example, consider something that you yourself have written: boost/yap/print.hpp: template <typename T, typename = void_t<>> struct printer { std::ostream & operator() (std::ostream & os, T const &) { return os << "<<unprintable-value>>"; } }; template <typename T> struct printer< T, void_t<decltype( std::declval<std::ostream &>() << std::declval<T const &>() )> > { std::ostream & operator() (std::ostream & os, T const & x) { return os << x; } }; Now consider a class that defines a stream operator separately from the class: // x.hpp class X {}; // x_print.hpp std::ostream& operator<<(std::ostream&, const X&); Next, I have two separate translation units: //a.cpp #include <x.hpp> #include <x_print.hpp> yap::detail::print_value(cout, X{}); // b.cpp #include <x.hpp> yap::detail::print_value(cout, X{}); printer chooses a different specialization in a.cpp than it does in b.cpp, which results in undefined behavior. As a result of this problem, I believe that any free functions (including operators) that are intended to be found by ADL *must* be declared alongside the class definition.
[snip]
Let me bring operator||/operator&& short circuiting back up. After implementing it, I don't think it's appropriate. Consider the current non-short-circuiting implementation on the boost_review branch:
https://github.com/tzlaine/yap/blob/boost_review/include/boost/yap/detail/de...
#define BOOST_YAP_BINARY_OPERATOR_CASE(op, op_name) \ template <> \ struct default_eval_expr_impl<expr_kind:: op_name> \ { \ template <typename Expr, typename ...T> \ decltype(auto) operator() (Expr && expr, T && ... args) \ { \ using namespace hana::literals; \ return \ default_eval_expr(static_cast<Expr &&>(expr).elements[0_c], static_cast<T &&>(args)...) op \ default_eval_expr(static_cast<Expr &&>(expr).elements[1_c], static_cast<T &&>(args)...); \ } \ };
This implementation is fine. The problem was the original implementation that called eval_ ## op_name, bypassing built-in short-circuiting.
If the "&&" in "default_eval_expr(...) && default_eval_expr(...)" resolves to a built-in operator&&(), short-circuiting will happen as always, right? But if the "&&" resolves to a user-defined operator&&(), let's say this one:
struct my_type { // ... std::shared_ptr<int> operator&&(my_type const & rhs) {/*...*/} };
then I really don't want to artificially impose the short-circuiting. The whole point of evaluate() is that it evaluates to whatever your Yap expression would have if it were a plain ol' non-Yap expression.
I agree with you. You don't need to add your own short-circuiting. You just need to not get in the way of the language's short-circuiting. In Christ, Steven Watanabe