Add a second cpp2::range constructor which takes 2 types, and deduce the common type for them (if available) (#1270)

* Add a `cpp2::range` ctor which takes 2 different types

Use a CTAD deduction guide to deduce the `std::common_type` for both types (if a common one exists).

This allows code like the following to compile without integer precision conversion warnings:
```
for 0 ..< vector.size() do (e) { ... }
```
since the integer literal 0 and the size expression evaluate as different signed/unsigned types.

* Update regression tests due to line number changes

* Merge results of rerunning regression on my machine

---------

Signed-off-by: Herb Sutter <[email protected]>
Co-authored-by: Herb Sutter <[email protected]>

Author: bluetarpmedia

include/cpp2util.h

@@ -746,6 +746,11 @@ concept valid_custom_is_operator = predicate_member_fun<X, F, &F::op_is>
                         || brace_initializable_to<X, argument_of_op_is_t<F>> 
                       );
 
+template <typename T, typename U>
+concept has_common_type = requires (T t, U u) {
+    typename std::common_type_t<T, U>;
+};
+
 //-----------------------------------------------------------------------
 //
 //  General helpers
@@ -2437,6 +2442,19 @@ class range
         }
     }
 
+    //  When the first & last types are different, use a CTAD deduction guide
+    //  to find the `std::common_type` for them, if one exists. See below
+    //  after the class definition for the deduction guide.
+    template <typename U>
+        requires has_common_type<T, U>
+    range(
+        T const& f,
+        U const& l,
+        bool     include_last = false
+    )
+        : range(f, l, include_last)
+    {}
+
     class iterator 
     {
         TT first = T{};
@@ -2572,6 +2590,16 @@ class range
     }
 };
 
+//  CTAD deduction guide for the `range` constructor that takes two different types.
+//  Deduces the `std::common_type` for them, if one exists.
+template <typename T, typename U>
+    requires has_common_type<T, U>
+range(
+    T const& f,
+    U const& l,
+    bool     include_last = false
+) -> range<std::common_type_t<T, U>>;
+
 template<typename T>
 constexpr auto contains(range<T> const& r, T const& t)
     -> bool

regression-tests/pure2-range-operators.cpp2

@@ -13,6 +13,11 @@ main: () = {
         std::cout << "  (e)$  (v[e])$\n";
     }
 
+    std::cout << "\nAnd test the range when mixing signed & unsigned types:\n";
+    for 0 ..< v.size() do (e) {
+        std::cout << "  (e)$  (v[e])$\n";
+    }
+
     all_about: std::list = 
         ( "Hokey", "Pokey" );
 

regression-tests/test-results/apple-clang-14-c++2b/pure2-last-use.cpp.output

@@ -0,0 +1,74 @@
+pure2-last-use.cpp2:273:36: error: expected variable name or 'this' in lambda capture list
+   public: std::add_pointer_t<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> g; 
+                                   ^
+pure2-last-use.cpp2:329:2: error: expected '>'
+};
+ ^
+pure2-last-use.cpp2:273:30: note: to match this '<'
+   public: std::add_pointer_t<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> g; 
+                             ^
+pure2-last-use.cpp2:344:16: error: no template named 'move_only_function' in namespace 'std'
+  public: std::move_only_function<int()> b; 
+          ~~~~~^
+pure2-last-use.cpp2:348:161: error: no member named 'move_only_function' in namespace 'std'
+CPP2_REQUIRES_ (std::is_convertible_v<CPP2_TYPEOF(a_), std::add_const_t<std::unique_ptr<int>>&> && std::is_convertible_v<CPP2_TYPEOF(b_), std::add_const_t<std::move_only_function<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(c_), std::add_const_t<std::add_lvalue_reference_t<int>>&>) ;
+                                                                                                                                                           ~~~~~^
+../../../include/cpp2util.h:10008:43: note: expanded from macro 'CPP2_REQUIRES_'
+    #define CPP2_REQUIRES_(...) requires (__VA_ARGS__)
+                                          ^~~~~~~~~~~
+pure2-last-use.cpp2:348:188: error: expected expression
+CPP2_REQUIRES_ (std::is_convertible_v<CPP2_TYPEOF(a_), std::add_const_t<std::unique_ptr<int>>&> && std::is_convertible_v<CPP2_TYPEOF(b_), std::add_const_t<std::move_only_function<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(c_), std::add_const_t<std::add_lvalue_reference_t<int>>&>) ;
+                                                                                                                                                                                           ^
+pure2-last-use.cpp2:348:193: error: use of address-of-label extension outside of a function body
+CPP2_REQUIRES_ (std::is_convertible_v<CPP2_TYPEOF(a_), std::add_const_t<std::unique_ptr<int>>&> && std::is_convertible_v<CPP2_TYPEOF(b_), std::add_const_t<std::move_only_function<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(c_), std::add_const_t<std::add_lvalue_reference_t<int>>&>) ;
+                                                                                                                                                                                                ^
+pure2-last-use.cpp2:773:69: error: no template named 'move_only_function' in namespace 'std'
+auto issue_888_1([[maybe_unused]] std::string unnamed_param_1, std::move_only_function<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> size) -> void;
+                                                               ~~~~~^
+pure2-last-use.cpp2:773:93: error: expected variable name or 'this' in lambda capture list
+auto issue_888_1([[maybe_unused]] std::string unnamed_param_1, std::move_only_function<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> size) -> void;
+                                                                                            ^
+pure2-last-use.cpp2:773:156: error: expected unqualified-id
+auto issue_888_1([[maybe_unused]] std::string unnamed_param_1, std::move_only_function<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> size) -> void;
+                                                                                                                                                           ^
+pure2-last-use.cpp2:773:160: error: expected '>'
+auto issue_888_1([[maybe_unused]] std::string unnamed_param_1, std::move_only_function<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> size) -> void;
+                                                                                                                                                               ^
+pure2-last-use.cpp2:773:87: note: to match this '<'
+auto issue_888_1([[maybe_unused]] std::string unnamed_param_1, std::move_only_function<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> size) -> void;
+                                                                                      ^
+pure2-last-use.cpp2:773:160: error: expected ')'
+auto issue_888_1([[maybe_unused]] std::string unnamed_param_1, std::move_only_function<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> size) -> void;
+                                                                                                                                                               ^
+pure2-last-use.cpp2:773:17: note: to match this '('
+auto issue_888_1([[maybe_unused]] std::string unnamed_param_1, std::move_only_function<int([[maybe_unused]] cpp2::impl::in<int> unnamed_param_1)> size) -> void;
+                ^
+pure2-last-use.cpp2:271:7: error: missing '}' at end of definition of 'issue_857_4'
+class issue_857_4 {
+      ^
+pure2-last-use.cpp2:905:1: note: still within definition of 'issue_857_4' here
+namespace captures {
+^
+pure2-last-use.cpp2:279:272: error: no member named 'move_only_function' in namespace 'std'
+requires (std::is_convertible_v<CPP2_TYPEOF(f_), std::add_const_t<std::add_pointer_t<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(g_), std::add_const_t<std::add_pointer_t<int(cpp2::impl::in<int> in_)>>&> && std::is_convertible_v<CPP2_TYPEOF(mf_), std::add_const_t<std::move_only_function<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(mg_), std::add_const_t<std::move_only_function<int(cpp2::impl::in<int> in_)>>&>) 
+                                                                                                                                                                                                                                                                          ~~~~~^
+pure2-last-use.cpp2:279:299: error: expected expression
+requires (std::is_convertible_v<CPP2_TYPEOF(f_), std::add_const_t<std::add_pointer_t<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(g_), std::add_const_t<std::add_pointer_t<int(cpp2::impl::in<int> in_)>>&> && std::is_convertible_v<CPP2_TYPEOF(mf_), std::add_const_t<std::move_only_function<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(mg_), std::add_const_t<std::move_only_function<int(cpp2::impl::in<int> in_)>>&>) 
+                                                                                                                                                                                                                                                                                                          ^
+pure2-last-use.cpp2:279:304: error: use of address-of-label extension outside of a function body
+requires (std::is_convertible_v<CPP2_TYPEOF(f_), std::add_const_t<std::add_pointer_t<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(g_), std::add_const_t<std::add_pointer_t<int(cpp2::impl::in<int> in_)>>&> && std::is_convertible_v<CPP2_TYPEOF(mf_), std::add_const_t<std::move_only_function<int()>>&> && std::is_convertible_v<CPP2_TYPEOF(mg_), std::add_const_t<std::move_only_function<int(cpp2::impl::in<int> in_)>>&>) 
+                                                                                                                                                                                                                                                                                                               ^
+pure2-last-use.cpp2:278:14: error: out-of-line definition of 'issue_857_4' does not match any declaration in 'issue_857_4'
+issue_857_4::issue_857_4(auto&& f_, auto&& g_, auto&& mf_, auto&& mg_)
+             ^~~~~~~~~~~
+pure2-last-use.cpp2:281:272: error: member initializer 'g' does not name a non-static data member or base class
+                                                                                                                                                                                                                                                                             , g{ CPP2_FORWARD(g_) }
+                                                                                                                                                                                                                                                                               ^~~~~~~~~~~~~~~~~~~~~
+pure2-last-use.cpp2:282:272: error: member initializer 'mf' does not name a non-static data member or base class
+                                                                                                                                                                                                                                                                             , mf{ CPP2_FORWARD(mf_) }
+                                                                                                                                                                                                                                                                               ^~~~~~~~~~~~~~~~~~~~~~~
+pure2-last-use.cpp2:283:272: error: member initializer 'mg' does not name a non-static data member or base class
+                                                                                                                                                                                                                                                                             , mg{ CPP2_FORWARD(mg_) }{}
+                                                                                                                                                                                                                                                                               ^~~~~~~~~~~~~~~~~~~~~~~
+fatal error: too many errors emitted, stopping now [-ferror-limit=]
+20 errors generated.

regression-tests/test-results/apple-clang-14-c++2b/pure2-range-operators.cpp.execution

@@ -15,6 +15,16 @@ And from indexes 1..=5 they are:
   4  Elephant
   5  Flicker
 
+And test the range when mixing signed & unsigned types:
+  0  Aardvark
+  1  Baboon
+  2  Cat
+  3  Dolphin
+  4  Elephant
+  5  Flicker
+  6  Grue
+  7  Wumpus
+
 Make sure non-random-access iterators work:
   Hokey
   Pokey

regression-tests/test-results/apple-clang-15-c++2b/mixed-bounds-check.cpp.execution

@@ -1 +1 @@
-../../../include/cpp2util.h(1103) decltype(auto) cpp2::impl::assert_in_bounds(auto &&, std::source_location) [arg = 5, x:auto = std::vector<int>]: Bounds safety violation: out of bounds access attempt detected - attempted access at index 5, [min,max] range is [0,4]
+../../../include/cpp2util.h(1108) decltype(auto) cpp2::impl::assert_in_bounds(auto &&, std::source_location) [arg = 5, x:auto = std::vector<int>]: Bounds safety violation: out of bounds access attempt detected - attempted access at index 5, [min,max] range is [0,4]

regression-tests/test-results/apple-clang-15-c++2b/mixed-bounds-safety-with-assert.cpp.execution

@@ -1 +1 @@
-../../../include/cpp2util.h(915) : Bounds safety violation
+../../../include/cpp2util.h(920) : Bounds safety violation

regression-tests/test-results/apple-clang-15-c++2b/mixed-initialization-safety-3-contract-violation.cpp.execution

@@ -1 +1 @@
-../../../include/cpp2util.h(915) : Contract violation: fill: value must contain at least count elements
+../../../include/cpp2util.h(920) : Contract violation: fill: value must contain at least count elements

regression-tests/test-results/apple-clang-15-c++2b/mixed-lifetime-safety-and-null-contracts.cpp.execution

@@ -1,2 +1,2 @@
 sending error to my framework... [dynamic null dereference attempt detected]
-from source location: ../../../include/cpp2util.h(994) decltype(auto) cpp2::impl::assert_not_null(auto &&, std::source_location) [arg:auto = int *&]
+from source location: ../../../include/cpp2util.h(999) decltype(auto) cpp2::impl::assert_not_null(auto &&, std::source_location) [arg:auto = int *&]

regression-tests/test-results/apple-clang-15-c++2b/pure2-assert-expected-not-null.cpp.execution

@@ -1 +1 @@
-../../../include/cpp2util.h(994) decltype(auto) cpp2::impl::assert_not_null(auto &&, std::source_location) [arg:auto = std::expected<int, bool>]: Null safety violation: std::expected has an unexpected value
+../../../include/cpp2util.h(999) decltype(auto) cpp2::impl::assert_not_null(auto &&, std::source_location) [arg:auto = std::expected<int, bool>]: Null safety violation: std::expected has an unexpected value

regression-tests/test-results/apple-clang-15-c++2b/pure2-assert-optional-not-null.cpp.execution

@@ -1 +1 @@
-../../../include/cpp2util.h(994) decltype(auto) cpp2::impl::assert_not_null(auto &&, std::source_location) [arg:auto = std::optional<int>]: Null safety violation: std::optional does not contain a value
+../../../include/cpp2util.h(999) decltype(auto) cpp2::impl::assert_not_null(auto &&, std::source_location) [arg:auto = std::optional<int>]: Null safety violation: std::optional does not contain a value