[lmi-commits] [lmi] odd/eraseme_limits 700e166 5/6: Define 'minmax' of an empty vector

[Greg Chicares]

branch: odd/eraseme_limits
commit 700e166fbecf1cc47d42c1e764115a55a36803ce
Author: Gregory W. Chicares <gchicares@sbcglobal.net>
Commit: Gregory W. Chicares <gchicares@sbcglobal.net>

    Define 'minmax' of an empty vector
    
    Akin to APL's ⌊/⍳0 and ⌈/⍳0, define the minimum (maximum) of an empty
    vector to be positive (negative) N for some "largest" N: here, whatever
    std::numeric_limits<T>::max() (min()) return. The intention is to use
    an identity element for std::max() (std::min()), so, for floating point,
    -∞ and ∞ would be better.
---
 miscellany.hpp      | 6 ++++++
 miscellany_test.cpp | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/miscellany.hpp b/miscellany.hpp
index 8ab6f06..cb803a7 100644
--- a/miscellany.hpp
+++ b/miscellany.hpp
@@ -102,7 +102,13 @@ class minmax
         }
 
     explicit minmax(std::vector<T> const& v)
+        :minmax {}
         {
+        if(v.empty())
+            {
+            return;
+            }
+
         auto const& extrema = std::minmax_element(v.begin(), v.end());
         minimum_ = *extrema.first ;
         maximum_ = *extrema.second;
diff --git a/miscellany_test.cpp b/miscellany_test.cpp
index 19e25ff..c92bec3 100644
--- a/miscellany_test.cpp
+++ b/miscellany_test.cpp
@@ -145,6 +145,12 @@ void test_minmax()
     LMI_TEST( DBL_MAX == dbl_minmax.minimum());
     LMI_TEST(-DBL_MAX == dbl_minmax.maximum());
 
+    // Test explicit ctor with zero-element argument.
+    std::vector<int> const empty_vector {};
+    minmax<int> const empty_minmax(empty_vector);
+    LMI_TEST_EQUAL(empty_minmax.minimum(), std::numeric_limits<int>::max());
+    LMI_TEST_EQUAL(empty_minmax.maximum(), std::numeric_limits<int>::min());
+
     // Test const-correctness.
     std::vector<double> const v = w;
     minmax<double> const m(v);