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gdb: make_scoped_restore and types convertible to T 

A following patch will want to do

   string_file str_file;

   scoped_restore save_stdout
    = make_scoped_restore (&gdb_stdout, &str_file);

where gdb_stdout is a ui_file *, and string_file is a type that
inherits from ui_file, but that doesn't compile today:

  src/gdb/top.c: In function ‘std::__cxx11::string execute_command_to_string(char*, int)’:
  src/gdb/top.c:710:50: error: no matching function for call to ‘make_scoped_restore(ui_file**, string_file*)’
       = make_scoped_restore (&gdb_stdout, &str_file);
						    ^
  [...]
  In file included from src/gdb/utils.h:25:0,
		   from src/gdb/defs.h:732,
		   from src/gdb/top.c:20:
  src/gdb/common/scoped_restore.h:94:24: note: candidate: template<class T> scoped_restore_tmpl<T> make_scoped_restore(T*, T)
   scoped_restore_tmpl<T> make_scoped_restore (T *var, T value)
			  ^
  src/gdb/common/scoped_restore.h:94:24: note:   template argument deduction/substitution failed:
  src/gdb/top.c:710:50: note:   deduced conflicting types for parameter ‘T’ (‘ui_file*’ and ‘string_file*’)
       = make_scoped_restore (&gdb_stdout, &str_file);
						    ^

This commit makes code such as the above possible.

gdb/ChangeLog:
2017-01-31  Pedro Alves  <palves@redhat.com>

	* common/scoped_restore.h
	(scoped_restore_tmpl::scoped_restore_tmpl): Template on T2, and
	change the value's parameter type to T2.
	(make_scoped_restore): Likewise.
This commit is contained in:
Pedro Alves 2017-01-31 17:56:35 +00:00
parent 1273da0414
commit 60adb36c08
2 changed files with 14 additions and 4 deletions
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7
gdb/ChangeLog
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@ -1,3 +1,10 @@
2017-01-31 Pedro Alves <palves@redhat.com>
* common/scoped_restore.h
(scoped_restore_tmpl::scoped_restore_tmpl): Template on T2, and
change the value's parameter type to T2.
(make_scoped_restore): Likewise.
2017-01-27 Walfred Tedeschi <walfred.tedeschi@intel.com>
Richard Henderson <rth@redhat.com>

11
gdb/common/scoped_restore.h
View File

@ -47,8 +47,11 @@ class scoped_restore_tmpl : public scoped_restore_base
/* Create a new scoped_restore object that saves the current value
of *VAR, and sets *VAR to VALUE. *VAR will be restored when this
scoped_restore object is destroyed. */
scoped_restore_tmpl (T *var, T value)
scoped_restore object is destroyed. This is templated on T2 to
allow passing VALUEs of types convertible to T.
E.g.: T='base'; T2='derived'. */
template <typename T2>
scoped_restore_tmpl (T *var, T2 value)
: m_saved_var (var),
m_saved_value (*var)
{
@ -90,8 +93,8 @@ scoped_restore_tmpl<T> make_scoped_restore (T *var)
/* Make a scoped_restore. This is useful because it lets template
argument deduction work. */
template<typename T>
scoped_restore_tmpl<T> make_scoped_restore (T *var, T value)
template<typename T, typename T2>
scoped_restore_tmpl<T> make_scoped_restore (T *var, T2 value)
{
return scoped_restore_tmpl<T> (var, value);
}