March 12, 2026
One Call, Infinite Drama
The Cost of Indirection in Rust
Rust coders clash: One extra call won’t kill speed, say vets; skeptics cry AI
TLDR: The post argues that breaking Rust tasks into helper functions rarely hurts speed because the compiler optimizes it; real delays come from I/O. Comments split between “profile it and chill,” AI-suspicion, and “premise is wrong,” with a shared lesson: measure before sacrificing clean, readable code.
The latest Rust blog drops a spicy claim: splitting big tasks into smaller helper functions won’t slow your app, because the compiler is smart and the real slowdown is waiting on stuff like the network. Cue the popcorn—comments erupted. One old‑timer admitted they’ve changed their mind since the early days of “boxed” async, but not everyone was buying it. A skeptic said they were “turned off by the obvious AI-isms,” throwing shade on the author’s credibility. Another commenter went straight for the jugular: “a function call isn’t necessarily indirection,” saying the blog’s basic premise is shaky. Meanwhile, a pragmatist summed up the vibe: check the machine code and run a benchmark. And a veteran voice reminded everyone we’ve had auto‑inlining for decades and that pointer chasing in memory is the real villain—not tidy helper calls.
In plain speak: you already pay a branch cost; adding a neat helper usually costs peanuts, especially when the compiler can fold it away. The blog even shows tiny test functions producing the same result in optimized builds, and points to tools like Compiler Explorer for proof. The crowd split into profile‑first realists and premise‑poking purists, with memes about obsessing over nanoseconds while your app waits milliseconds on the network. Verdict: write clean code, then measure.
Key Points
- •Extracting large async logic into a separate function in Rust usually adds negligible overhead in practice.
- •Rust’s compiler often flattens async calls by merging the callee’s state into the caller’s Future state machine.
- •Match arms already incur a branch; adding a function call typically adds minimal extra cost (another jump and frame setup).
- •I/O, locks, and allocations dominate runtime compared to the few cycles of a function call, especially in async paths.
- •With release optimizations, small extracted functions are often inlined, producing assembly identical to inline versions.