bindings: cxx: make operator bool() explicit

A non-explicit operator bool() is dangerous: It allows unwanted
conversion to integral types:

gpiod::chip c;
int i = c;

This is a trivial example, but more insidious effects are possible,
e.g. with std::set<gpiod::chip>, which would use the operator bool()
to implement element comparison, thus turning such set into a set that
has at most 2 elements: An invalid (false) element and just 1 valid
element:

std::set<gpiod::chip> s;
s.emplace();
s.emplace("/dev/gpiochip0");
s.emplace("/dev/gpiochip1");
// s.size() is still 2 even if both chips were opened!

Making the operator explicit disables this.

See e.g.
https://en.cppreference.com/w/cpp/language/implicit_conversion#The_safe_bool_problem
for more info on this.

Signed-off-by: David Kozub <zub@linux.fjfi.cvut.cz>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

diff --git a/bindings/cxx/gpiod.hpp b/bindings/cxx/gpiod.hpp
index b92597f03316a0a0989b9a517d16e3c481ac5eee..cf4489bf5fc6dff19407adf3a3cfd5d49f2e08ae 100644 (file)
--- a/bindings/cxx/gpiod.hpp
+++ b/bindings/cxx/gpiod.hpp
@@ -167,7 +167,7 @@ public:
         * @brief Check if this object holds a reference to a GPIO chip.
         * @return True if this object references a GPIO chip, false otherwise.
         */
-       GPIOD_API operator bool(void) const noexcept;
+       GPIOD_API explicit operator bool(void) const noexcept;
 
        /**
         * @brief Check if this object doesn't hold a reference to a GPIO chip.
@@ -422,7 +422,7 @@ public:
         * @brief Check if this object holds a reference to any GPIO line.
         * @return True if this object references a GPIO line, false otherwise.
         */
-       GPIOD_API operator bool(void) const noexcept;
+       GPIOD_API explicit operator bool(void) const noexcept;
 
        /**
         * @brief Check if this object doesn't reference any GPIO line.
@@ -630,7 +630,7 @@ public:
         * @brief Check if this object holds any lines.
         * @return True if this line_bulk holds at least one line, false otherwise.
         */
-       GPIOD_API operator bool(void) const noexcept;
+       GPIOD_API explicit operator bool(void) const noexcept;
 
        /**
         * @brief Check if this object doesn't hold any lines.

diff --git a/bindings/cxx/line.cpp b/bindings/cxx/line.cpp
index 9f5454ceb4513c19ad8eb750af291af5dbab658c..989976e72a655722157b9c6f81969b20d84b5402 100644 (file)
--- a/bindings/cxx/line.cpp
+++ b/bindings/cxx/line.cpp
@@ -147,7 +147,7 @@ bool line::event_wait(const ::std::chrono::nanoseconds& timeout) const
 
        line_bulk event_bulk = bulk.event_wait(timeout);
 
-       return ::std::move(event_bulk);
+       return !!event_bulk;
 }
 
 line_event line::event_read(void) const