[lmi-commits] [lmi] master 6084765 2/3: Revert "Serve cached file reads as non-const [...] shared_ptr"

[Greg Chicares]

branch: master
commit 6084765925d2503cfbbae1c289672d94f44fbd98
Author: Gregory W. Chicares <gchicares@sbcglobal.net>
Commit: Gregory W. Chicares <gchicares@sbcglobal.net>

    Revert "Serve cached file reads as non-const [...] shared_ptr"
    
    This reverts most of commit a202f8754d3b9bf728078203e87c469190753ce4,
    which was misbegotten: it removed 'const' just to make some unit tests
    work without 'const_cast'. Cf.:
      https://lists.nongnu.org/archive/html/lmi/2016-08/msg00006.html
    | I think the way I'd do this would be to provide a way to test such
    | what-if scenario in product_database itself by allowing to replace
    | its "db_" member.
---
 cache_file_reads.hpp | 10 +++++-----
 database.cpp         |  4 ++--
 database.hpp         |  2 +-
 input_test.cpp       |  2 +-
 premium_tax_test.cpp |  2 +-
 5 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/cache_file_reads.hpp b/cache_file_reads.hpp
index 5591730..0229420 100644
--- a/cache_file_reads.hpp
+++ b/cache_file_reads.hpp
@@ -47,11 +47,11 @@ namespace detail
 /// For each filename, the cache stores one instance, which is
 /// replaced by reloading the file if its write time has changed.
 ///
-/// Instances are retrieved as shared_ptr<T> so that they remain
+/// Instances are retrieved as shared_ptr<T const> so that they remain
 /// valid even when the file changes. The client is responsible for
-/// updating any stale pointers it holds. An earlier version returned
-/// shared_ptr<T const> instead, but legitimate non-const use cases
-/// exist, so managing constness is better left to each client.
+/// updating any stale pointers it holds, if it chooses to refresh the
+/// data; if it doesn't, then it uses older data, which remain valid
+/// as long as it holds a pointer to them.
 ///
 /// Implemented as a simple Meyers singleton, with the expected
 /// dead-reference and threading issues.
@@ -60,7 +60,7 @@ template<typename T>
 class file_cache
 {
   public:
-    using retrieved_type = std::shared_ptr<T>;
+    using retrieved_type = std::shared_ptr<T const>;
 
     static file_cache<T>& instance()
         {
diff --git a/database.cpp b/database.cpp
index 6cecf32..91e99b9 100644
--- a/database.cpp
+++ b/database.cpp
@@ -170,7 +170,7 @@ namespace
 ///
 /// Postcondition: returned pointer is not null; throws otherwise.
 
-std::shared_ptr<DBDictionary> antediluvian_db()
+std::shared_ptr<DBDictionary const> antediluvian_db()
 {
     std::shared_ptr<DBDictionary> z(new DBDictionary);
     z->InitAntediluvian();
@@ -187,7 +187,7 @@ void product_database::initialize(std::string const& 
product_name)
 {
     if(is_antediluvian_fork())
         {
-        static std::shared_ptr<DBDictionary> z(antediluvian_db());
+        static std::shared_ptr<DBDictionary const> z(antediluvian_db());
         db_ = z;
         }
     else
diff --git a/database.hpp b/database.hpp
index daca9d8..236d308 100644
--- a/database.hpp
+++ b/database.hpp
@@ -101,7 +101,7 @@ class LMI_SO product_database final
     int                  length_;
     int                  maturity_age_;
 
-    std::shared_ptr<DBDictionary> db_;
+    std::shared_ptr<DBDictionary const> db_;
 };
 
 /// Query database, using default index; return a scalar.
diff --git a/input_test.cpp b/input_test.cpp
index 0fe0673..464b30e 100644
--- a/input_test.cpp
+++ b/input_test.cpp
@@ -101,7 +101,7 @@ void input_test::test_product_database()
     Input input;
     yare_input yi(input);
     product_database db(yi);
-    DBDictionary& dictionary = *db.db_;
+    DBDictionary& dictionary = const_cast<DBDictionary&>(*db.db_);
 
     std::vector<double> v;
     std::vector<double> w;
diff --git a/premium_tax_test.cpp b/premium_tax_test.cpp
index 442dacf..288fd1f 100644
--- a/premium_tax_test.cpp
+++ b/premium_tax_test.cpp
@@ -99,7 +99,7 @@ void premium_tax_test::test_rates()
     // A uniform but nonzero load would elicit a runtime error,
     // because the tiered load is not zero.
     {
-    DBDictionary& dictionary = *db.db_;
+    DBDictionary& dictionary = const_cast<DBDictionary&>(*db.db_);
 
     database_entity const original = dictionary.datum("PremTaxLoad");
     database_entity const scalar(DB_PremTaxLoad, 0.0000);