FTL: Add FTL_EXPECT
Like FTL_TRY, FTL_EXPECT unwraps T for Expected<T, E> or does an early
out on error, but it bails out with E instead of Expected<T, E>.
Fix a line in the Expected.Try test to call the intended helper.
Bug: 185536303
Test: ftl_test
Change-Id: I238ae2978ff606c5c035e9791496c2b20729ca7f
diff --git a/include/ftl/expected.h b/include/ftl/expected.h
index 57448dc..7e765c5 100644
--- a/include/ftl/expected.h
+++ b/include/ftl/expected.h
@@ -69,6 +69,36 @@
exp_.value(); \
})
+// Given an expression `expr` that evaluates to an ftl::Expected<T, E> result (R for short),
+// FTL_EXPECT unwraps T out of R, or bails out of the enclosing function F if R has an error E.
+// While FTL_TRY bails out with R, FTL_EXPECT bails out with E, which is useful when F does not
+// need to propagate R because T is not relevant to the caller.
+//
+// Example usage:
+//
+// using StringExp = ftl::Expected<std::string, std::errc>;
+//
+// std::errc repeat(StringExp exp, std::string& out) {
+// const std::string str = FTL_EXPECT(exp);
+// out = str + str;
+// return std::errc::operation_in_progress;
+// }
+//
+// std::string str;
+// assert(std::errc::operation_in_progress == repeat(StringExp("ha"s), str));
+// assert("haha"s == str);
+// assert(std::errc::bad_message == repeat(ftl::Unexpected(std::errc::bad_message), str));
+// assert("haha"s == str);
+//
+#define FTL_EXPECT(expr) \
+ ({ \
+ auto exp_ = (expr); \
+ if (!exp_.has_value()) { \
+ return std::move(exp_.error()); \
+ } \
+ exp_.value(); \
+ })
+
namespace android::ftl {
// Superset of base::expected<T, E> with monadic operations.
diff --git a/libs/ftl/expected_test.cpp b/libs/ftl/expected_test.cpp
index 9b7f017..d5b1d7e 100644
--- a/libs/ftl/expected_test.cpp
+++ b/libs/ftl/expected_test.cpp
@@ -79,16 +79,28 @@
namespace {
-IntExp increment(IntExp exp) {
+IntExp increment_try(IntExp exp) {
const int i = FTL_TRY(exp);
return IntExp(i + 1);
}
-StringExp repeat(StringExp exp) {
+std::errc increment_expect(IntExp exp, int& out) {
+ const int i = FTL_EXPECT(exp);
+ out = i + 1;
+ return std::errc::operation_in_progress;
+}
+
+StringExp repeat_try(StringExp exp) {
const std::string str = FTL_TRY(exp);
return StringExp(str + str);
}
+std::errc repeat_expect(StringExp exp, std::string& out) {
+ const std::string str = FTL_EXPECT(exp);
+ out = str + str;
+ return std::errc::operation_in_progress;
+}
+
void uppercase(char& c, ftl::Optional<char> opt) {
c = std::toupper(FTL_TRY(std::move(opt).ok_or(ftl::Unit())));
}
@@ -97,13 +109,13 @@
// Keep in sync with example usage in header file.
TEST(Expected, Try) {
- EXPECT_EQ(IntExp(100), increment(IntExp(99)));
- EXPECT_TRUE(repeat(ftl::Unexpected(std::errc::value_too_large)).has_error([](std::errc e) {
+ EXPECT_EQ(IntExp(100), increment_try(IntExp(99)));
+ EXPECT_TRUE(increment_try(ftl::Unexpected(std::errc::value_too_large)).has_error([](std::errc e) {
return e == std::errc::value_too_large;
}));
- EXPECT_EQ(StringExp("haha"s), repeat(StringExp("ha"s)));
- EXPECT_TRUE(repeat(ftl::Unexpected(std::errc::bad_message)).has_error([](std::errc e) {
+ EXPECT_EQ(StringExp("haha"s), repeat_try(StringExp("ha"s)));
+ EXPECT_TRUE(repeat_try(ftl::Unexpected(std::errc::bad_message)).has_error([](std::errc e) {
return e == std::errc::bad_message;
}));
@@ -115,4 +127,19 @@
EXPECT_EQ(c, 'A');
}
+TEST(Expected, Expect) {
+ int i = 0;
+ EXPECT_EQ(std::errc::operation_in_progress, increment_expect(IntExp(99), i));
+ EXPECT_EQ(100, i);
+ EXPECT_EQ(std::errc::value_too_large,
+ increment_expect(ftl::Unexpected(std::errc::value_too_large), i));
+ EXPECT_EQ(100, i);
+
+ std::string str;
+ EXPECT_EQ(std::errc::operation_in_progress, repeat_expect(StringExp("ha"s), str));
+ EXPECT_EQ("haha"s, str);
+ EXPECT_EQ(std::errc::bad_message, repeat_expect(ftl::Unexpected(std::errc::bad_message), str));
+ EXPECT_EQ("haha"s, str);
+}
+
} // namespace android::test