GeezerVison

Consider a map with a std::string as the key type, for example mapping an HTTP route to its handler:

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std::unordered_map<std::string, Handler const*> handlers;

What actually happens when you try to look things up in this map? Let’s say that you want to test it with handlers.find("/api/v2/accounts/positions/summary"). This code will compile and run quite happily, but under the hood this allocates the literal into an entirely new std::string object, hashes it, finds the value, and then throws the temporary string away.

In C++ tuples are implemented as library feature rather than as language feature. As a consequence of that, we are syntactically limited by what the language offers.

This means rather than being able to subscript tuples directly, we need to use std::get<N>(tup) instead.

So… if we step a bit outside of the boundaries of the standard, can we subscript instead?

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auto tup = nonstd::tuple(1, 'c', 3.2);
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f(tup[0], tup[2]);

This can happen if you attempt to use P1061 pack-introducing structured bindings outside of a template:

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void f() {
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  // error: pack declaration outside of template
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  auto [...Is] = expr;
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}

To avoid turning f itself into a template, you can use P1306 expansion statements. Unlike lambda solutions, this does not push another function scope.