Argument-type declarations **normally have no impact on performance**: regardless of what argument types (if any) are declared, Julia compiles a specialized version of the function for the actual argument types passed by the caller. For example, calling `fib(1)` will trigger the compilation of specialized version of `fib` optimized specifically for `Int` arguments, which is then re-used if `fib(7)` or `fib(15)` are called. (There are rare exceptions when an argument-type declaration can trigger additional compiler specializations; see: [Be aware of when Julia avoids specializing](@ref).) The most common reasons to declare argument types in Julia are, instead:
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