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gmock-actions: improve comments and tests for the implicit cast in Return.

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Commit a070cbd91c added an implicit cast to this path but didn't leave a very
clear explanation for why it was desirable, a clear example, or even test
coverage. Add a better comment and a test that fails when the implicit cast is
removed.

PiperOrigin-RevId: 444871311
Change-Id: I127982fa8d5bce9b6d1b68177c12dc0709449164
This commit is contained in:
Aaron Jacobs
2022-04-27 08:48:35 -07:00
committed by Copybara-Service
parent c144d78f82
commit 830fb56728
2 changed files with 39 additions and 7 deletions
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31
googlemock/test/gmock-actions_test.cc
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@@ -667,6 +667,37 @@ TEST(ReturnTest, SupportsWrapperReturnType) {
EXPECT_THAT(result, ::testing::ElementsAre(0, 1, 2, 3, 4));
}
TEST(ReturnTest, PrefersConversionOperator) {
// Define types In and Out such that:
//
// * In is implicitly convertible to Out.
// * Out also has an explicit constructor from In.
//
struct In;
struct Out {
int x;
explicit Out(const int x) : x(x) {}
explicit Out(const In&) : x(0) {}
};
struct In {
operator Out() const { return Out{19}; } // NOLINT
};
// Assumption check: the C++ language rules are such that a function that
// returns Out which uses In a return statement will use the implicit
// conversion path rather than the explicit constructor.
EXPECT_THAT([]() -> Out { return In(); }(), Field(&Out::x, 19));
// Return should work the same way: if the mock function's return type is Out
// and we feed Return an In value, then the Out should be created through the
// implicit conversion path rather than the explicit constructor.
MockFunction<Out()> mock;
EXPECT_CALL(mock, Call).WillOnce(Return(In()));
EXPECT_THAT(mock.AsStdFunction()(), Field(&Out::x, 19));
}
// Tests that Return(v) is covaraint.
struct Base {