Magic statics vs. std::call_once

This article discusses two methods for caching results in C++: using magic statics and std::call_once. It compares their convenience and accessibility across multiple functions.

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bool should_use_widgets() { bool supported = ⟦ complex code to check OS features ⟧; return supported && is_configuration_enabled("widgets"); } Since OS Widget support is not something that changes during the lifetime of the program, you want to calculate it once and cache the result.

One way is to use a so-called “magic static”:

bool should_use_widgets() { static const bool supported = [] { return ⟦ complex code to check OS features ⟧; }(); return supported && is_configuration_enabled("widgets"); } Function-local statics are initialized the first time execution reaches the variable. On subsequent executions, nothing happens.

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