[PATCH] D105014: added some example code for llvm::Expected<T>
Christian Kühnel via Phabricator via cfe-commits
cfe-commits at lists.llvm.org
Wed Jun 30 02:37:51 PDT 2021
kuhnel updated this revision to Diff 355485.
kuhnel marked 2 inline comments as done.
kuhnel added a comment.
fixed compilation issues
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D105014/new/
https://reviews.llvm.org/D105014
Files:
llvm/include/llvm/Support/Error.h
llvm/include/llvm/Testing/Support/Error.h
Index: llvm/include/llvm/Testing/Support/Error.h
===================================================================
--- llvm/include/llvm/Testing/Support/Error.h
+++ llvm/include/llvm/Testing/Support/Error.h
@@ -165,6 +165,29 @@
#define ASSERT_THAT_ERROR(Err, Matcher) \
ASSERT_THAT(llvm::detail::TakeError(Err), Matcher)
+/// Helper marcro for checking the result of an 'Expected<T>'
+///
+/// @code{.cpp}
+/// // function to be tested
+/// Expected<int> myDivide(int A, int B);
+///
+/// TEST(myDivideTests, GoodAndBad) {
+/// // test the good care
+/// auto D1 = myDivide(10, 5);
+/// // ensure the Error gets consumed in case the function fails by
+/// // calling 'toString()'. This also helps in debugging failing tests.
+/// EXPECT_THAT_EXPECTED(D1, Succeeded()) << toString(D1.takeError()) <<
+/// "\n";
+/// EXPECT_THAT(*D1, Eq(2));
+///
+/// // test the error case
+/// auto D2 = myDivide(10, 0);
+/// EXPECT_THAT_EXPECTED(D2, Failed());
+/// // In the error case we need to consume the error.
+/// consumeError(D2.takeError());
+/// }
+/// @endcode
+
#define EXPECT_THAT_EXPECTED(Err, Matcher) \
EXPECT_THAT(llvm::detail::TakeExpected(Err), Matcher)
#define ASSERT_THAT_EXPECTED(Err, Matcher) \
Index: llvm/include/llvm/Support/Error.h
===================================================================
--- llvm/include/llvm/Support/Error.h
+++ llvm/include/llvm/Support/Error.h
@@ -436,6 +436,39 @@
/// Error cannot be copied, this class replaces getError() with
/// takeError(). It also adds an bool errorIsA<ErrT>() method for testing the
/// error class type.
+///
+/// Example usage of 'Expected<T>' as a function return type:
+///
+/// @code{.cpp}
+/// Expected<int> myDivide(int A, int B) {
+/// if (B == 0) {
+/// // return an Error
+/// return createStringError(inconvertibleErrorCode(),
+/// "B must not be zero!");
+/// }
+/// // return an integer
+/// return A / B;
+/// }
+/// @endcode
+///
+/// Checking the results of to a function returning 'Expected<T>':
+/// @code{.cpp}
+/// if (auto E = Result.takeError()) {
+/// // We must consume the error. Typically one of:
+/// // - return the error to our caller
+/// // - toString(), when logging
+/// // - consumeError(), to silently swallow the error
+/// // - handleErrors(), to distinguish error types
+/// errs() << "Problem with division " << toString(std::move(E)) << "\n";
+/// return;
+/// }
+/// // use the result
+/// outs() << "The answer is " << *Result << "\n";
+/// @endcode
+///
+/// For unit-testing a function returning an 'Expceted<T>', see the
+/// 'EXPECT_THAT_EXPECTED' macros in llvm/Testing/Support/Error.h
+
template <class T> class LLVM_NODISCARD Expected {
template <class T1> friend class ExpectedAsOutParameter;
template <class OtherT> friend class Expected;
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