C++17 in Detail: A Deep Dive/

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if constexpr

if constexpr

The lesson explains why 'if constexpr' should be used, and how it is different from simple if statements.

We'll cover the following...

Th​is is a big one! The compile-time if for C++!

The feature allows you to discard branches of an if statement at compile-time based on a constant expression condition.

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 if constexpr (cond)
        statement1; // Discarded if cond is false
    else
        statement2; // Discarded if cond is true

For Example:

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template <typename T>
auto get_value(T t)
{
  if constexpr (std::is_pointer_v<T>)
    return *t;
  else
    return t;
}

if constexpr has the potential to simplify a lot of template code - especially when tag dispatching, SFINAE or preprocessor techniques are used.

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