https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100493
Bug ID: 100493
Summary: Lambda default copy capture that captures "this"
cannot be used in both C++17 and C++20 modes
Product: gcc
Version: 10.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: a...@cloudius-systems.com
Target Milestone: ---
Consider the following masterpiece:
struct a {
int b;
void f(int x) {
(void)[=] { (void)(b + x); };
}
};
The C++20 compiler wants me to disambiguate the [=] capture to mean either [=,
this] or [=, *this]:
<source>:6:15: warning: implicit capture of 'this' via '[=]' is deprecated in
C++20 [-Wdeprecated]
6 | (void)[=] { (void)(b + x); };
| ^
<source>:6:15: note: add explicit 'this' or '*this' capture
Humoring it, I add ", this" to the capture list:
struct a {
int b;
void f(int x) {
(void)[=, this] { (void)(b + x); };
}
};
This works in C++20 mode, but in C++17 mode, I get:
source>:6:19: warning: explicit by-copy capture of 'this' redundant with
by-copy capture default
6 | (void)[=, this] { (void)(b + x); };
| ^~~~
These warnings are either always on, or enabled by -Wdeprecated. Given I want
-Wdeprecated for other deprecated features, it's impossible for me to write
similar code that works in both C++17 and C++20.
Perhaps the C++20 warning can be moved to a separate flag, to allow library
code that targets both C++17 and C++20.
