Use variants to support objects as semantic values.

[bison.git] / ChangeLog

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+2008-11-03  Akim Demaille  <demaille@gostai.com>
+
+       Use variants to support objects as semantic values.
+       This patch was inspired by work by Michiel De Wilde.  But he used Boost
+       variants which (i) requires Boost on the user side, (ii) is slow, and
+       (iii) has useless overhead (the parser knows the type of the semantic value
+       there is no reason to duplicate this information as Boost.Variants do).
+       
+       This implementation reserves a buffer large enough to store the largest
+       objects.  yy::variant implements this buffer.  It was implemented with
+       Quentin Hocquet.
+       
+       * src/output.c (type_names_output): New.
+       (output_skeleton): Invoke it.
+       * data/c++.m4 (b4_variant_if): New.
+       (b4_symbol_value): If needed, provide a definition for variants.
+       * data/lalr1.cc (b4_symbol_value, b4_symbol_action_)
+       (b4_symbol_variant, _b4_char_sizeof_counter, _b4_char_sizeof_dummy)
+       (b4_char_sizeof, yy::variant): New.
+       (parser::parse): If variants are requested, define
+       parser::union_type, parser::variant, change the definition of
+       semantic_type, construct $$ before running the user action instead
+       of performing a default $$ = $1.
+       * examples/variant.yy: New.
+       Based on an example by Michiel De Wilde.
+
 2008-11-03  Akim Demaille  <demaille@gostai.com>
 
        Parameterize the extraction of semantic values.