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-rw-r--r--build2/variable.cxx6
-rw-r--r--build2/variable.hxx11
-rw-r--r--build2/variable.ixx35
3 files changed, 47 insertions, 5 deletions
diff --git a/build2/variable.cxx b/build2/variable.cxx
index ce88712..9ce9fe8 100644
--- a/build2/variable.cxx
+++ b/build2/variable.cxx
@@ -533,6 +533,8 @@ namespace build2
return s;
}
+ const string& value_traits<string>::empty_instance = empty_string;
+
const char* const value_traits<string>::type_name = "string";
const value_type value_traits<string>::value_type
@@ -585,6 +587,8 @@ namespace build2
throw_invalid_argument (n, r, "path");
}
+ const path& value_traits<path>::empty_instance = empty_path;
+
const char* const value_traits<path>::type_name = "path";
const value_type value_traits<path>::value_type
@@ -630,6 +634,8 @@ namespace build2
throw_invalid_argument (n, r, "dir_path");
}
+ const dir_path& value_traits<dir_path>::empty_instance = empty_dir_path;
+
const char* const value_traits<dir_path>::type_name = "dir_path";
const value_type value_traits<dir_path>::value_type
diff --git a/build2/variable.hxx b/build2/variable.hxx
index c5e1a13..9a58584 100644
--- a/build2/variable.hxx
+++ b/build2/variable.hxx
@@ -289,6 +289,12 @@ namespace build2
template <typename T> const T* cast_null (const value&);
template <typename T> const T* cast_null (const lookup&);
+ // As above but returns empty value if the value is NULL (or not defined, in
+ // case of lookup).
+ //
+ template <typename T> const T& cast_empty (const value&);
+ template <typename T> const T& cast_empty (const lookup&);
+
// As above but returns false/true if the value is NULL (or not defined,
// in case of lookup). Note that the template argument is only for
// documentation and should be bool (or semantically compatible).
@@ -433,6 +439,8 @@ namespace build2
// //
// static const bool empty_value = true;
//
+ // static const T empty_instance;
+ //
// // For simple types (those that can be used as elements of containers),
// // type_name must be constexpr in order to sidestep the static init
// // order issue (in fact, that's the only reason we have it both here
@@ -579,6 +587,7 @@ namespace build2
static bool empty (const string& x) {return x.empty ();}
static const bool empty_value = true;
+ static const string& empty_instance;
static const char* const type_name;
static const build2::value_type value_type;
};
@@ -608,6 +617,7 @@ namespace build2
static bool empty (const path& x) {return x.empty ();}
static const bool empty_value = true;
+ static const path& empty_instance;
static const char* const type_name;
static const build2::value_type value_type;
};
@@ -628,6 +638,7 @@ namespace build2
static bool empty (const dir_path& x) {return x.empty ();}
static const bool empty_value = true;
+ static const dir_path& empty_instance;
static const char* const type_name;
static const build2::value_type value_type;
};
diff --git a/build2/variable.ixx b/build2/variable.ixx
index 6126a4e..634e3dc 100644
--- a/build2/variable.ixx
+++ b/build2/variable.ixx
@@ -187,21 +187,46 @@ namespace build2
}
template <typename T>
- inline T
- cast_false (const value& v) {return v && cast<T> (v);}
+ inline const T&
+ cast_empty (const value& v)
+ {
+ return v ? cast<T> (v) : value_traits<T>::empty_instance;
+ }
+
+ template <typename T>
+ inline const T&
+ cast_empty (const lookup& l)
+ {
+ return l ? cast<T> (l) : value_traits<T>::empty_instance;
+ }
template <typename T>
inline T
- cast_false (const lookup& l) {return l && cast<T> (l);}
+ cast_false (const value& v)
+ {
+ return v && cast<T> (v);
+ }
template <typename T>
inline T
- cast_true (const value& v) {return !v || cast<T> (v);}
+ cast_false (const lookup& l)
+ {
+ return l && cast<T> (l);
+ }
template <typename T>
inline T
- cast_true (const lookup& l) {return !l || cast<T> (l);}
+ cast_true (const value& v)
+ {
+ return !v || cast<T> (v);
+ }
+ template <typename T>
+ inline T
+ cast_true (const lookup& l)
+ {
+ return !l || cast<T> (l);
+ }
template <typename T>
inline void