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Re: Why is the advanced config object read-only?


On 29/04/2019 12:41, John Beard wrote:

Then you might start running into consistency issues with multiple
users of A_C getting different answers.

Notably, there is a specific case that illustrates where global state can cause Bad Things (TM) right now: unit tests.

Say you had a mutable ADVANCED_CFG, and you have a test suite like this:

        CONNECTIVITY_FOO thing;
        ADVANCED_CFG::GetCfg().m_whatever = true; // default false

        thing.Frobnicate(); // cares about m_whatever

        // what is ADVANCED_CFG::GetCfg().m_whatever?
        // It depends on the test case ordering.
// Test2 does not *have* to come second, and might even be concurrent
        // so AC::m_whatever could even change *during* this test

        CONNECTIVITY_FOO thing;
        thing.Frobnicate(); // what will this do?

Also, if core functions depend on A_C, it's very hard to test them with good coverage. It's better to pass the A_C as a higher level parameter, so you can do this:

    BOOST_AUTO_TEST_CASE( TestWithFeatureOn )
        bool enable_feature = true;
        CONNECTIVITY_FOO thing( enable_feature );
        thing.Frobnicate(); // test with feature

    BOOST_AUTO_TEST_CASE( TestWithFeatureOff )
        bool enable_feature = false;
        CONNECTIVITY_FOO thing( enable_feature );
        thing.Frobnicate(); // test without feature

If CONNECTIVITY_FOO only used A_C internally, you cannot test the feature reliably as it depends on the config the user has set.



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