Idiomatic Mojo Habits
Write code that is fast by default.
Idiomatic Mojo Habits is a free Mojo Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Mojo Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Fast by Default
The best speed comes from habits, not last-minute tricks. Idiomatic Mojo is written so it is fast from the very first draft. 🚀
Prefer fn in Hot Paths
Reach for fn in code that runs often. Its required types let the compiler optimize the parts of your program that matter most.
fn dot(a: Int, b: Int) -> Int:
return a * bAnnotate Your Types
Spell out types on values and arguments. Each annotation removes a runtime guess and helps Mojo emit faster machine code.
var total: Int = 0
var ratio: Float64 = 0.5Declare with var
Use var for clear, explicit variables inside fn code. Predictable scope helps both the compiler and the next reader.
fn run():
var n = 10
print(n)Lean on Value Semantics
Mojo's value semantics avoid surprise sharing. Let values own their data so your code stays correct without defensive copying.
Borrow When Reading
Pass big values as borrowed when you only read them. You avoid a copy while keeping the original safe and unchanged.
fn show(borrowed data: Int):
print(data)Vectorize Number Crunching
For element-wise math, reach for SIMD so the CPU handles many values per instruction instead of one slow scalar at a time.
var v = SIMD[DType.float32, 4](1, 2, 3, 4)Reuse Python Where It Fits
Keep mature libraries via interop, but cross the bridge rarely. Do heavy loops in Mojo and call Python for the parts it already nails.
from python import PythonMeasure Before Tuning
Profile first so you optimize the real hot path. Guessing wastes effort on code that was never slowing you down.
Keep Loops Tight
Move setup and allocations outside the loop. A tight inner loop with no extra work is what the compiler optimizes best.
var buf = List[Int]()
for i in range(100):
buf.append(i)Readable Stays Fast
Idiomatic Mojo is clear and fast at once. You rarely sacrifice readability for speed, because good habits give you both.
Quick Check
Pick the habit that keeps Mojo fast by default.
Recap
Idiomatic Mojo uses typed fn in hot paths, borrows to read, vectorizes math, and profiles first. Good habits make code fast and clear. 🎯
Frequently asked questions
Is the “Idiomatic Mojo Habits” lesson free?
Yes — the full text of “Idiomatic Mojo Habits” is free to read here on the web, and the Mojo Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Mojo Academy course, upgrade to CoddyKit PRO.
What will I learn in “Idiomatic Mojo Habits”?
Write code that is fast by default. You practise Mojo Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Mojo Academy?
No prior experience is required. Mojo Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Idiomatic Mojo Habits” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Mojo Academy lesson?
Yes. Every Mojo Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Writing a Fair Benchmark
- Why fn and Types Speed Up
- Reading the Numbers Honestly
- Idiomatic Mojo Habits