MemSpan: Fix MemSpan<void> to not construct from arrays of constant values.

Author: SolidWallOfCode

code/include/swoc/MemSpan.h

@@ -138,7 +138,7 @@ template <typename T> class MemSpan {
    *
    * @internal A non-const variant of this is needed because passing by CR means imposing constness
    * on the container which can then undesirably propagate that to the element type. Best example -
-   * consstructing from @c std::string. Without this variant it's not possible to construct a @c char
+   * constructing from @c std::string. Without this variant it's not possible to construct a @c char
    * span vs. a @c char @c const.
    */
   template < typename C
@@ -1369,7 +1369,9 @@ constexpr MemSpan<void const>::MemSpan(U (&a)[N]) : _ptr(const_cast<std::remove_
   }
 }
 template <auto N, typename U>
-constexpr MemSpan<void>::MemSpan(U (&a)[N]) : super_type(a) {}
+constexpr MemSpan<void>::MemSpan(U (&a)[N]) : super_type(a) {
+  static_assert(!std::is_const_v<U>, "Error: constructing non-constant view with constant data.");
+}
 
 template <typename C, typename>
 constexpr MemSpan<void const>::MemSpan(C const &c)

unit_tests/test_MemSpan.cc

@@ -148,8 +148,9 @@ TEST_CASE("MemSpan modifiers", "[libswoc][MemSpan]") {
     REQUIRE(0 == memcmp(span.clip_suffix(5), MemSpan<void>(post - 5, 5)));
     REQUIRE(0 == memcmp(span, MemSpan<void>(pre, text.size() - 5)));
 
-    MemSpan<void> s1{"Evil Dave Rulz"};
-    REQUIRE(s1.size() == 14); // terminal nul is not in view.
+    // By design, MemSpan<void> won't construct from a literal string because it's const.
+    // MemSpan<void> s1{"Evil Dave Rulz"}; // Should not compile.
+
     uint8_t bytes[]{5,4,3,2,1,0};
     MemSpan<void> s2{bytes};
     REQUIRE(s2.size() == sizeof(bytes)); // terminal nul is in view
@@ -195,9 +196,6 @@ TEST_CASE("MemSpan construct", "[libswoc][MemSpan]") {
   REQUIRE(span[4]._n == 56);
   span.destroy();
   REQUIRE(counter == 0);
-
-  MemSpan<void const> vc_span { "Evil Dave Rulz"};
-  // MemSpan<void> v_span { "Evil Dave Rulz" }; // This should not compile.
 }
 
 TEST_CASE("MemSpan<void>", "[libswoc][MemSpan]")