The Go language was tweaked slightly to permit the variable to be omitted in a range clause, so that one can write "for range v" instead of having to write "for _ = range v". This patch from Chris Manghane implements this in gccgo. Bootstrapped and ran Go testsuite on x86_64-unknown-linux-gnu. Committed to mainline.
Ian
diff -r 569e72035892 go/parse.cc --- a/go/parse.cc Wed Oct 08 07:02:06 2014 -0700 +++ b/go/parse.cc Thu Oct 09 16:33:58 2014 -0700 @@ -3836,6 +3836,12 @@ this->unget_token(Token::make_identifier_token(identifier, is_exported, location)); } + else if (p_range_clause != NULL && token->is_keyword(KEYWORD_RANGE)) + { + Typed_identifier_list til; + this->range_clause_decl(&til, p_range_clause); + return NULL; + } Expression* exp = this->expression(PRECEDENCE_NORMAL, true, may_be_composite_lit, @@ -5278,7 +5284,7 @@ } } -// RangeClause = IdentifierList ( "=" | ":=" ) "range" Expression . +// RangeClause = [ IdentifierList ( "=" | ":=" ) ] "range" Expression . // This is the := version. It is called with a list of identifiers. @@ -5291,7 +5297,6 @@ p_range_clause->found = true; - go_assert(til->size() >= 1); if (til->size() > 2) error_at(this->location(), "too many variables for range clause"); @@ -5300,6 +5305,9 @@ NULL); p_range_clause->range = expr; + if (til->empty()) + return; + bool any_new = false; const Typed_identifier* pti = &til->front(); @@ -5347,6 +5355,9 @@ p_range_clause->range = this->expression(PRECEDENCE_NORMAL, false, false, NULL, NULL); + if (vals->empty()) + return; + p_range_clause->index = vals->front(); if (vals->size() == 1) p_range_clause->value = NULL; diff -r 569e72035892 go/statements.cc --- a/go/statements.cc Wed Oct 08 07:02:06 2014 -0700 +++ b/go/statements.cc Thu Oct 09 16:33:58 2014 -0700 @@ -5305,8 +5305,12 @@ int For_range_statement::do_traverse(Traverse* traverse) { - if (this->traverse_expression(traverse, &this->index_var_) == TRAVERSE_EXIT) - return TRAVERSE_EXIT; + if (this->index_var_ != NULL) + { + if (this->traverse_expression(traverse, &this->index_var_) + == TRAVERSE_EXIT) + return TRAVERSE_EXIT; + } if (this->value_var_ != NULL) { if (this->traverse_expression(traverse, &this->value_var_) @@ -5434,25 +5438,27 @@ if (iter_init != NULL) body->add_statement(Statement::make_block_statement(iter_init, loc)); - Statement* assign; - Expression* index_ref = Expression::make_temporary_reference(index_temp, loc); - if (this->value_var_ == NULL) + if (this->index_var_ != NULL) { - assign = Statement::make_assignment(this->index_var_, index_ref, loc); + Statement* assign; + Expression* index_ref = + Expression::make_temporary_reference(index_temp, loc); + if (this->value_var_ == NULL) + assign = Statement::make_assignment(this->index_var_, index_ref, loc); + else + { + Expression_list* lhs = new Expression_list(); + lhs->push_back(this->index_var_); + lhs->push_back(this->value_var_); + + Expression_list* rhs = new Expression_list(); + rhs->push_back(index_ref); + rhs->push_back(Expression::make_temporary_reference(value_temp, loc)); + + assign = Statement::make_tuple_assignment(lhs, rhs, loc); + } + body->add_statement(assign); } - else - { - Expression_list* lhs = new Expression_list(); - lhs->push_back(this->index_var_); - lhs->push_back(this->value_var_); - - Expression_list* rhs = new Expression_list(); - rhs->push_back(index_ref); - rhs->push_back(Expression::make_temporary_reference(value_temp, loc)); - - assign = Statement::make_tuple_assignment(lhs, rhs, loc); - } - body->add_statement(assign); body->add_statement(Statement::make_block_statement(this->statements_, loc));