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MDEV-22441 implement a generic way to change a value of a variable in a scope

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Example:
{
  auto _= make_scope_value(var, tmp_value);
}

make_scope_value(): a function which returns RAII object which temporary
changes a value of a variable

detail::Scope_value: actual implementation of such RAII class.
It shouldn't be used directly! That's why it's inside a namespace detail.
This commit is contained in:
Eugene Kosov 2025-01-13 15:40:58 +03:00 committed by Aleksey Midenkov
parent b337e14440
commit 52dd489515
3 changed files with 51 additions and 4 deletions
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45
include/scope.h
View File

@ -72,3 +72,48 @@ make_scope_exit(Callable &&f)
#define ANONYMOUS_VARIABLE CONCAT(_anonymous_variable, __LINE__)
#define SCOPE_EXIT auto ANONYMOUS_VARIABLE= make_scope_exit
namespace detail
{
template <typename T> class Scope_value
{
public:
Scope_value(T &variable, const T &scope_value)
: variable_(variable), saved_value_(variable)
{
variable= scope_value;
}
Scope_value(Scope_value &&rhs)
: variable_(rhs.variable_), saved_value_(rhs.saved_value_),
engaged_(rhs.engaged_)
{
rhs.engaged_= false;
}
Scope_value(const Scope_value &)= delete;
Scope_value &operator=(const Scope_value &)= delete;
Scope_value &operator=(Scope_value &&)= delete;
~Scope_value()
{
if (engaged_)
variable_= saved_value_;
}
private:
T &variable_;
T saved_value_;
bool engaged_= true;
};
} // namespace detail
// Use like this:
// auto _= make_scope_value(var, tmp_value);
template <typename T>
detail::Scope_value<T> make_scope_value(T &variable, const T &scope_value)
{
return detail::Scope_value<T>(variable, scope_value);
}

6
sql/sql_acl.cc
View File

@ -54,6 +54,7 @@
#include "sql_array.h"
#include "sql_hset.h"
#include "password.h"
#include "scope.h"
#include "sql_plugin_compat.h"
#include "wsrep_mysqld.h"
@ -2552,10 +2553,11 @@ static bool acl_load(THD *thd, const Grant_tables& tables)
{
READ_RECORD read_record_info;
char tmp_name[SAFE_NAME_LEN+1];
Sql_mode_save old_mode_save(thd);
DBUG_ENTER("acl_load");
thd->variables.sql_mode&= ~MODE_PAD_CHAR_TO_FULL_LENGTH;
auto _= make_scope_value(thd->variables.sql_mode,
thd->variables.sql_mode &
~MODE_PAD_CHAR_TO_FULL_LENGTH);
grant_version++; /* Privileges updated */

4
sql/sql_show.cc
View File

@ -65,6 +65,7 @@
#include "transaction.h"
#include "opt_trace.h"
#include "my_cpu.h"
#include "scope.h"
#include "lex_symbol.h"
@ -6437,8 +6438,7 @@ bool store_schema_params(THD *thd, TABLE *table, TABLE *proc_table,
{
Field *field;
LEX_CSTRING tmp_string;
Sql_mode_save sql_mode_backup(thd);
thd->variables.sql_mode= sql_mode;
auto _= make_scope_value(thd->variables.sql_mode, sql_mode);
if (sph->type() == SP_TYPE_FUNCTION)
{