Table Alternate Codes – Operators/Functions

The alternate codes map will be implemented in a number of steps including adding alternate codes automatically for operators and internal functions, using the alternate map for operators and functions, removing the associated codes for operators and functions, manually adding alternate codes for internal codes, using the alternate map for internal codes, and adding additional alternate codes (to further reduce the need for code enumerators).

First, the definition for the alternate code static map member was added to the table class along with its instantiation in the table source file.  The standard array is new to the C++11 STL and is just as efficient as a built-in array with improvements.  Since the definition is quite lengthy, it was broken into two definitions (there was no reason to define a constant for the 3 since this is the only place that it is needed; indicating up to three operands or arguments):

using EntryVectorArray = std::array<std::vector<TableEntry *>, 3>;
static std::unordered_map<TableEntry *, EntryVectorArray> s_alternate;

The add function was modified to add an entry as an alternate code if appropriate.  Alternate codes are based on having the same name as another code.  If an entry name is newly added to the name to entry static map, then the routine returns immediately, in other words, the code is a primary code.  If the name is already in this map, has an expression information structure, has operands, and does not have its Reference flag set, then the entry can be added as an alternate code.

If the operand count of the entry is less than the count of the primary code, then it should be the primary code.  In this case, the pointer to the entry replaces the value in the name to entry map, and the previous primary is made an alternate code of the entry, by adding to the array element for its operand count minus one, and returning.  This was a better solution then reporting an error.

The routine does a series of comparisons between the operand data types of the entry with that of the primary to identify which primary code it should be added as an alternate to.  If all the operand data types of the primary code match that of entry and the entry is an internal function with more operands, then it is made an alternate of the primary in the array element one less than the operand count.  This is a multiple argument entry (ASC, INSTR or MID$) so the Multiple flag is set on the primary code.  Otherwise, the entry has duplicate operands as the primary and an error is thrown.

Since the Multiple flag is set automatically, it no longer needs to be specified in the table entry array initialization.  Also since this is automatic, and the requirement that a multiple entry be in the following entry in the table was eliminated, the validation of multiple non-assignment entries was removed from the table constructor.

Using the debugger within QtCreator, the alternate map was verified to be setup correctly.  At this point however, this new alternate map is not being used.  This will be the subject of the next change, which will be to use the alternate map for the operators and internal functions instead of the associated code arrays.

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