CODEWITHSUNDEEP
c++constexpr
ChrisMM
ChrisMM

Reputation: 10103

Conditionally constexpr variable

I have a bunch tests for a project which were originally written using Gtest, but I have since moved them into Microsoft's CppUnitTestFramework. In order to prevent having to rewrite all my tests, I made macros which follows how GTest does its tests -- for example, EXPECT_EQ.

Now, I am trying to eliminate all warnings generated by MsBuild, including those by the Code Analysis, which relate to using constexpr if available. In the tests, there's quite a few of these, since the expected value is usually a literal, although not always. So I have my own EXPECT_EQ which is as follows:

#define EXPECT_EQ( x, y ) { const auto _x = (x); const auto _y = (y); if ( _x == _y ) {} else { Assert::Fail(createFailMessage( _x, L" == ", _y ).c_str(), LINE_INFO() ); } }

This works fine; however, if it is called with EXPECT_EQ( 7, getTime() ), then I get a warning about how _x can be constexpr.

I know I can just create a separate macro like so:

#define EXPECT_CEQ( x, y ) { constexpr auto _x = (x); const auto _y = (y); if ( _x == _y ) {} else { Assert::Fail(createFailMessage( _x, L" == ", _y ).c_str(), LINE_INFO() ); } }

However, if I go back to GTest later, then I would have to fix all my tests to change EXPECT_CEQ to EXPECT_EQ.

So, my question is, is it possible to combine these two macros to make _x conditionally constexpr based on whether or not it can be constexpr?

PS: Yes, I know, macros bad.

Upvotes: 2

Views: 164

Answers (1)

Evg
Evg

Reputation: 26362

One possible solution is to use a lambda that is invoked immediately:

const auto _x = [&]{ return (x); }();

[&] will capture every variable that might be used in the x expression.

Upvotes: 3

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