[PATCH 1/5] gdb: make_scoped_restore and types convertible to T

Pedro Alves
2017-01-17T01:39:12Z

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:
2017-01-17 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.
---
gdb/common/scoped_restore.h | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/gdb/common/scoped_restore.h b/gdb/common/scoped_restore.h
index 0c8c30d..ae7a49f 100644
--- a/gdb/common/scoped_restore.h
+++ b/gdb/common/scoped_restore.h
@@ -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);
}
--
2.5.5