Add macros M_LET_IF and M_DEFER to help handling with runtime errors

README.md

@@ -5913,14 +5913,65 @@ then the variable 'v1' will be initialized with the
 contains of 'va_list...' using the specialized initializer operator INIT\_WITH
 and not the empty initializer INIT operator.
 
+There shall be at most one M\_LET macro per line of source code.
+
 Example:
 
      M_LET(a, STRING_OPLIST) { do something with a }  or
      M_LET(a, b, c, STRING_OPLIST) { do something with a, b & c }
 
-NOTE: The user code can not perform a return or a goto outside the {}
+NOTE: The user code shall not perform a return or a goto (or longjmp) outside the {} or a call to an exit function
 otherwise the clear code of the object won't be called .
-However, you can use the break instruction to quit the block.
+However, you can use the break instruction to quit the block (the clear function will be exexcuted),
+and you can chain the M\_LET macro to create several different variables.
+
+
+##### M\_LET\_IF(init_code, test_code, clear_code)
+
+This macro defines the variable(s) in 'init_code',
+executes the next block of instructions where the variable(s) is(are) used if the initialization succeeds by testing 'test_code',
+then it executes the 'clear_code'.
+
+'test_code' returns a boolean indicating if the initialization succeeds (true) or not.
+If the initialization fails, it won't call the 'clear_code'.
+
+The syntax is the same as a for loop.
+
+There shall be at most one M\_LET\_IF macro per line of source code.
+
+Example:
+
+    M_LET_IF(int *p = malloc(100), p!=0, free(p)) {
+      M_LET_IF( /* nothing */ , mtx_lock(&mut)!=thrd_error, mtx_unlock(&mut)) {
+        printf ("OK! Let's use p in a mutex section\n");
+      }
+    }
+
+NOTE:
+The user code shall not perform a return or a goto (or longjmp) outside the {} or a call to an exit function
+otherwise the clear_code won't be called .
+However, you can use the break instruction to quit the block (the clear_code will be exexcuted),
+and you can chain the M\_LET macro to create several different variables.
+
+##### M\_DEFER(clear_code)
+
+This macro registers the execution of 'clear_code' when reaching the further closing brace
+of the next block of instruction.
+
+There shall be at most one M\_DEFER macro per line of source code.
+
+Example:
+
+        m_mutex_lock(mut);
+        M_DEFER(m_mutex_unlock(mut)) {
+            // Use of the critical section.
+        }
+
+NOTE:
+The user code shall not perform a return or a goto (or longjmp) outside the {} or a call to an exit function
+otherwise the clear_code won't be called .
+You can use the break instruction to quit the block (the clear_code will be exexcuted),
+and you can chain the M\_LET macro to create several different variables.
 
 
 #### Memory / Error macros

m-core.h

@@ -3117,14 +3117,50 @@ m_core_parse2_enum (const char str[], const char **endptr)
 
 /* Transform the va list by adding their number as the first argument of
    the list.
-   Example:   M_VA(a,b,c,d,e) ==> 5,a,b,c,d,e */
+   Example:   M_VA(a,b,c,d,e) ==> 5,a,b,c,d,e
+   TODO: Use of a structure instead of an integer to ensure limited syntax control.
+*/
 #define M_VA(...) M_NARGS(__VA_ARGS__), __VA_ARGS__
 
 
-/* Initialize the container 'dest' as per 'oplist'
-   and fill it with the given VA arguments.
-   NOTE: If the REVERSE operator exists, it is a list, 
-   so reverse the final order.
+/* Defer the evaluation of the given expression until the closing brace.
+   M_DEFER(code) { }
+   Example:
+     M_DEFER(free(p)) {
+             // code using p
+     } // Here p is free
+*/
+#define M_DEFER(clear)                                                        \
+  M_DEFER_INTERNAL(clear, m_var_ ## __LINE__)
+
+#define M_DEFER_INTERNAL(clear, cont)                                         \
+  for(bool cont = true; cont; cont = false)                                   \
+    for( (void) 0; cont ; (clear))                                            \
+      for( (void) 0; cont; cont = false)                                      \
+
+
+/* Declare a variable, initialize it, continue if the initialization succeeds,
+   and clears the variable afterwards.
+   Otherwise, stop the execution.
+   M_LET_IF(init code, test code, clear code) { code using the variable }
+   Example:
+   M_LET_IF(void * p = malloc(100), p!=0, free(p)) {
+      // code using p
+   } // Here p is free
+*/
+#define M_LET_IF(init, test, clear)                                           \
+  M_LET_IF_INTERNAL(init, test, clear, m_var_ ## __LINE__)
+
+#define M_LET_IF_INTERNAL(init, test, clear, cont)                            \
+  for(bool cont = true; cont; cont = false)                                   \
+    for( init ; cont && (test) ; (clear))                                     \
+      for( (void) 0; cont; cont = false)                                      \
+
+
+/* Initialize the container 'dest' as per 'oplist' INIT operator
+   and fill it with the given VA arguments with the PUSH operator.
+   NOTE: If the REVERSE operator exists, it assumes a list,
+   so it reverses the final order.
 */
 #define M_INIT_VAI(oplist, dest, ...)                                         \
   (void)(M_GET_INIT oplist (dest) ,                                           \
@@ -3134,8 +3170,11 @@ m_core_parse2_enum (const char str[], const char **endptr)
 #define M_INIT_VAI_FUNC(d, a)                                                 \
   M_PAIR_2 d (M_PAIR_1 d, a)
 
-/* Initialize the container 'dest' as per 'oplist'
-   and fill it with the given VA arguments which are pair of (key,value) */
+
+/* Initialize the container 'dest' as per 'oplist' INIT operator
+   and fill it with the given VA argument
+   assumed to be pair (key,value) with the SET_KEY operator.
+*/
 #define M_INIT_KEY_VAI(oplist, dest, ...)                                     \
   (void)(M_GET_INIT oplist (dest) ,                                           \
          M_MAP2_C(M_INIT_KEY_VAI_FUNC, (dest, M_GET_SET_KEY oplist) , __VA_ARGS__))

tests/test-mcore.c

@@ -192,6 +192,27 @@ static void test_let(void)
     assert(0);
   }
   assert(b);
+
+  int c = 0;
+  M_LET_IF( assert(c++ == 0), (assert(c++ == 1), true), assert(c++ == 3)) {
+    assert(c++ == 2);
+  }
+  M_LET_IF( assert(c++ == 4), (assert(c++ == 5), false), assert(0)) {
+    assert(0);
+  }
+  assert(c++ == 6);
+  M_LET_IF(int *p = (int*) malloc(sizeof(int)), p!=0, free(p)) {
+    assert(p != NULL);
+    *p = 4;
+  }
+
+  int *p = (int*)malloc(sizeof(int));
+  assert(p != NULL);
+  M_DEFER ( (assert(c++ == 8), free(p)) ) {
+    *p = 4;
+    assert(c++ == 7);
+  }
+  assert(c++ == 9);
 }
 
 static void test_va(void)