What do you do when the code for a variable initialization is complicated? Do you move it to another method or write inside the current scope?
In this blog post, I’d like to present a trick that allows computing a value for a variable, even a const variable, with a compact notation.

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IIFE (Immediately-Invoked Function Expression) is a technique in C++ that uses lambdas to initialize const variables with complex multi-line logic. Instead of dropping const and writing mutable initialization code inline, you wrap the logic in a lambda and immediately call it. The post covers syntax, readability improvements via named lambdas or std::invoke(), capture list best practices (prefer explicit captures over [&]), a C++26 update that allows omitting empty parentheses, a practical HTML string-building example, and a benchmark showing ~10% performance gain from increased const usage.

IIFE for Complex Initialization

Should we capture the whole context with & ?