[RFA 2/4] Change the as_*_interp functions to use dynamic_cast

[Tom Tromey <tom@tromey.com>]

This changes the various as_*_interp functions to be implemented using
dynamic_cast.  I believe this is a small improvement, because it is
more typesafe -- the C++ runtime does the type-checking for us.

ChangeLog
2018-04-29  Tom Tromey  <tom@tromey.com>

	* tui/tui-interp.c (as_tui_interp): Use dynamic_cast.
	* mi/mi-interp.c (as_mi_interp): Use dynamic_cast.
	* cli/cli-interp.c (as_cli_interp): Use dynamic_cast.
---
 gdb/ChangeLog        | 6 ++++++
 gdb/cli/cli-interp.c | 4 +---
 gdb/mi/mi-interp.c   | 4 +---
 gdb/tui/tui-interp.c | 4 +---
 4 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/gdb/cli/cli-interp.c b/gdb/cli/cli-interp.c
index 0663301c19..e12d45b4b7 100644
--- a/gdb/cli/cli-interp.c
+++ b/gdb/cli/cli-interp.c
@@ -73,9 +73,7 @@ struct cli_suppress_notification cli_suppress_notification =
 static struct cli_interp *
 as_cli_interp (struct interp *interp)
 {
-  if (strcmp (interp_name (interp), INTERP_CONSOLE) == 0)
-    return (struct cli_interp *) interp;
-  return NULL;
+  return dynamic_cast<cli_interp *> (interp);
 }
 
 /* Longjmp-safe wrapper for "execute_command".  */
diff --git a/gdb/mi/mi-interp.c b/gdb/mi/mi-interp.c
index 8bfb1298a5..7536817f43 100644
--- a/gdb/mi/mi-interp.c
+++ b/gdb/mi/mi-interp.c
@@ -106,9 +106,7 @@ display_mi_prompt (struct mi_interp *mi)
 static struct mi_interp *
 as_mi_interp (struct interp *interp)
 {
-  if (interp_ui_out (interp)->is_mi_like_p ())
-    return (struct mi_interp *) interp;
-  return NULL;
+  return dynamic_cast<mi_interp *> (interp);
 }
 
 void
diff --git a/gdb/tui/tui-interp.c b/gdb/tui/tui-interp.c
index cf32c905c5..aa5e328ded 100644
--- a/gdb/tui/tui-interp.c
+++ b/gdb/tui/tui-interp.c
@@ -58,9 +58,7 @@ public:
 static tui_interp *
 as_tui_interp (struct interp *interp)
 {
-  if (strcmp (interp_name (interp), INTERP_TUI) == 0)
-    return (tui_interp *) interp;
-  return NULL;
+  return dynamic_cast<tui_interp *> (interp);
 }
 
 /* Cleanup the tui before exiting.  */
-- 
2.13.6