Probably Dance

Here’s a neat little trick that one of my co-workers, Clint Levijoki, discovered. In C++ you often use an RAII wrapper that you place on the stack if you want to be sure that code gets run at a later point. One good example would be std::lock_guard which you use if you want to be sure that a lock gets released in the future, or scoped profiling which you use to stop a timer in the future. For example for this:

std::string foo();
void bar()
{
    std::string baz = foo();
    // do something with baz
}

If you want to profile foo() you’d write it like this:

std::string foo();
void bar()
{
    std::string baz;
    {
        ScopedProfiler profile_foo("foo()");
        baz = foo();
    }
    // do something with baz
}

Which is less pretty and slightly slower. Alternatively you can use the comma operator and do it like this:

std::string foo();
void bar()
{
    std::string baz = (ScopedProfiler("foo()"), foo());
    // do something with baz
}

And this will start a timer before calling foo(), and stop the timer after calling foo(). You could wrap it in a macro to make it more readable. And the benefit is obviously that you don’t have to destroy your function flow when you want to insert RAII objects.

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