Allow generation of EMPLACE_TYPE

for variant if all oplists defined a FIELD operator.

README.md

@@ -624,6 +624,7 @@ The following classic operators are usually expected for an object:
 Other documented operators are:
 
 * `NAME()` --> `prefix`: Return the base name `prefix` used to construct the container.
+* `FIELD()` --> `field name`: Return the name of the field used when constructing the container.
 * `TYPE()` --> `type`: Return the base type associated to this oplist.
 * `SUBTYPE()` --> `type`: Return the type of the element stored in the container (used to iterate over the container).
 * `GENTYPE()` --> `type`: Return the type representing TYPE suitable for a _Generic statement.

m-core.h

@@ -3386,6 +3386,7 @@ M_INLINE size_t m_core_cstr_hash(const char str[])
 #define M_GENTYPE_GENTYPE(a)     ,a,
 #define M_SUBTYPE_PTR_SUBTYPE_PTR(a) ,a,
 #define M_NAME_NAME(a)           ,a,
+#define M_FIELD_FIELD(a)         ,a,
 #define M_OPLIST_OPLIST(a)       ,a,
 #define M_SORT_SORT(a)           ,a,
 #define M_SPLICE_BACK_SPLICE_BACK(a) ,a,
@@ -3477,6 +3478,7 @@ M_INLINE size_t m_core_cstr_hash(const char str[])
 #define M_GET_SUBTYPE_PTR(...) M_GET_METHOD(SUBTYPE_PTR, M_NO_DEF_SUBTYPE_PTR, __VA_ARGS__)
 #define M_GET_GENTYPE(...)   M_GET_METHOD(GENTYPE,     M_NO_DEF_GENTYPE,   __VA_ARGS__)
 #define M_GET_NAME(...)      M_GET_METHOD(NAME,        M_NO_DEF_NAME,      __VA_ARGS__)
+#define M_GET_FIELD(...)     M_GET_METHOD(FIELD,       M_NO_DEF_FIELD,     __VA_ARGS__)
 #define M_GET_OPLIST(...)    M_GET_METHOD(OPLIST,      (),                 __VA_ARGS__)
 #define M_GET_SORT(...)      M_GET_METHOD(SORT,        M_NO_DEF_SORT,      __VA_ARGS__)
 #define M_GET_SPLICE_BACK(...) M_GET_METHOD(SPLICE_BACK, M_NO_DEF_SPLICE_BACK, __VA_ARGS__)
@@ -3558,6 +3560,7 @@ M_INLINE size_t m_core_cstr_hash(const char str[])
 //#define M_CALL_SUBTYPE_PTR(oplist, ...) M_APPLY_API(M_GET_SUBTYPE_PTR oplist, oplist, __VA_ARGS__)
 //#define M_CALL_GENTYPE(oplist, ...) M_APPLY_API(M_GET_GENTYPE oplist, oplist, __VA_ARGS__)
 //#define M_CALL_NAME(oplist, ...) M_APPLY_API(M_GET_NAME oplist, oplist, __VA_ARGS__)
+//#define M_CALL_FIELD(oplist, ...) M_APPLY_API(M_GET_FIELD oplist, oplist, __VA_ARGS__)
 //#define M_CALL_OPLIST(oplist, ...) M_APPLY_API(M_GET_OPLIST oplist, oplist, __VA_ARGS__)
 #define M_CALL_SORT(oplist, ...) M_APPLY_API(M_GET_SORT oplist, oplist, __VA_ARGS__)
 #define M_CALL_SPLICE_BACK(oplist, ...) M_APPLY_API(M_GET_SPLICE_BACK oplist, oplist, __VA_ARGS__)

m-variant.h

@@ -194,9 +194,10 @@
   typedef                                                                     \
   M_IF_METHOD(GENTYPE, M_VAR1ANT_GET_OPLIST a)( M_GET_GENTYPE M_VAR1ANT_GET_OPLIST a, M_VAR1ANT_GET_TYPE a) \
   M_C4(m_var1ant_, name, _gentype_, num);                                     \
-  typedef const                                                               \
-  M_IF_METHOD(GENTYPE, M_VAR1ANT_GET_OPLIST a)( M_GET_GENTYPE M_VAR1ANT_GET_OPLIST a, M_VAR1ANT_GET_TYPE a) \
-  M_C4(m_var1ant_, name, _const_gentype_, num);
+  typedef                                                               \
+  M_IF_METHOD(GENTYPE, M_VAR1ANT_GET_OPLIST a)( const M_GET_GENTYPE M_VAR1ANT_GET_OPLIST a, M_VAR1ANT_GET_TYPE a const) \
+  M_C4(m_var1ant_, name, _const_gentype_, num); \
+  typedef M_VAR1ANT_GET_TYPE a M_C4(m_var1ant_, name, _type_, M_VAR1ANT_GET_FIELD a);
 
 #define M_VAR1ANT_DEFINE_UNION_ELE(name, a)                                   \
   , M_C4(name, _, M_VAR1ANT_GET_FIELD a, _value)
@@ -793,8 +794,19 @@ M_INLINE void                                                                 \
    M_IF_METHOD_ALL(INIT_MOVE, __VA_ARGS__)(INIT_MOVE(M_F(name, _init_move)),), \
    M_IF_METHOD_ALL(INIT_MOVE, __VA_ARGS__)(MOVE(M_F(name, _move)),),          \
    M_IF_METHOD_ALL(SWAP, __VA_ARGS__)(SWAP(M_F(name, _swap)),),               \
+   M_IF_METHOD_ALL(FIELD, __VA_ARGS__)(M_VAR1ANT_OPLIST_EMPLACE_TYPE(name, __VA_ARGS__),), \
    )
 
+/* Expand to an EMPLACE_TYPE compatible with OPLIST definition
+   (Use M_REDUCE2 which is already used by M_IF_METHOD_ALL)
+ */
+#define M_VAR1ANT_OPLIST_EMPLACE_TYPE(name, ...) EMPLACE_TYPE( LIST(          \
+ M_REDUCE2(M_VAR1ANT_OPLIST_EMPLACE_TYPE_EXPAND, M_ID, name, __VA_ARGS__)     \
+                                                                   ))
+#define M_VAR1ANT_OPLIST_EMPLACE_TYPE_EXPAND(name, oplist)      \
+  ( M_C(_, M_GET_FIELD oplist), M_C4(name, _init_set_, M_GET_FIELD oplist),     \
+    M_C4(m_var1ant_, name, _type_, M_GET_FIELD oplist) )
+
 
 /********************************** INTERNAL *********************************/