In this lesson, you will learn how to use symbol counters to pinpoint exactly which generic functions are causing your Rust binary to grow unexpectedly.
When you use generics, the Rust compiler performs "monomorphization"—creating a unique machine code version of a function for every concrete type you use. While this makes your code fast, it can lead to "bloat," where a single function is duplicated dozens of times in your final executable.
Identifying the Culprits
To see this in action, we use a tool called cargo-bloat. It acts as a symbol counter, scanning your compiled binary to report which functions take up the most space.
First, install the tool via cargo install cargo-bloat. Then, run it in your project directory:
cargo bloat --release --crates
This command breaks down the size contribution of every crate. If you suspect a specific generic function, you can look for individual symbols:
cargo bloat --release --limit 20
Analyzing the Output
When you run cargo bloat, you will see a list of functions sorted by size. Look for names that contain long, complex type signatures. For example, you might see my_crate::process_data<u32> and my_crate::process_data<i32> appearing as separate entries.
If you see the same generic function name repeated many times with different types, that is a clear signal that the compiler is generating redundant machine code for each variation. Once you identify these heavy hitters, you have a few tactical options based on what we’ve learned: you might decide to move the logic into a non-generic helper function, use #[inline(never)] to force a single implementation (if the generic type isn't strictly necessary for performance), or switch to trait objects for those specific parts of the program.
By using symbol counters, you stop guessing why your binary is large and start making data-driven decisions about where to apply abstraction and where to favor simplicity.
Key Takeaway: Use cargo-bloat to count symbols and identify redundant monomorphizations, allowing you to selectively refactor the specific generic functions that are inflating your binary size.