Higher-Order Functions and Currying
Pass, return, and partially apply functions.
Higher-Order Functions and Currying is a free Dart Academy lesson on CoddyKit — lesson 1 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 Dart Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Functions Are Values
In Dart, a function is just a value you can store in a variable. That single idea unlocks the whole world of functional patterns. 🎯
int square(int x) => x * x;
var op = square;
print(op(4)); // 16What Higher-Order Means
A higher-order function is one that takes a function as an argument or returns a function. You have already used them with list methods.
Passing a Function In
When you pass behavior as an argument, the caller decides what happens. Here apply runs whatever function it receives.
int apply(int v, int Function(int) f) => f(v);
print(apply(5, (x) => x + 1)); // 6Function Type Syntax
The type int Function(int) reads as: a function taking an int and returning an int. Types make your intent crystal clear.
void run(String Function(String) format) {
print(format('hi'));
}Returning a Function
A higher-order function can also return a function. The returned function remembers the values around it when it was created.
Function makeAdder(int n) {
return (int x) => x + n;
}Using the Returned Function
Call the maker once to build a specialized function, then reuse it. Each result is its own little configured tool.
var add10 = makeAdder(10);
print(add10(5)); // 15
print(add10(1)); // 11Meet Currying
Currying turns a multi-argument function into a chain of single-argument functions. You supply one value at a time.
int Function(int) add(int a) => (int b) => a + b;
print(add(3)(4)); // 7Partial Application
Fix the first argument now and the rest later. This is partial application, and it makes reusable, pre-loaded helpers.
var add3 = add(3);
print(add3(10)); // 13
print(add3(20)); // 23Why Curry at All
Currying lets you build specialized functions from general ones without rewriting logic. It shines when you compose small pipelines.
Functions as Parameters Type
You can name complex function types with a typedef to keep signatures readable across your code.
typedef IntOp = int Function(int);
int apply(int v, IntOp f) => f(v);Tear-Off Shortcut
Instead of wrapping a method in a lambda, pass its name directly. This tear-off keeps calls clean and tidy.
['1', '2', '3'].map(int.parse).forEach(print);Quick Check
Let us check your grasp of higher-order functions.
Recap
Functions are values, so you can pass and return them. Currying and partial application turn general functions into specialized tools. Nice work! 🚀
Frequently asked questions
Is the “Higher-Order Functions and Currying” lesson free?
Yes — the full text of “Higher-Order Functions and Currying” is free to read here on the web, and the Dart 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 Dart Academy course, upgrade to CoddyKit PRO.
What will I learn in “Higher-Order Functions and Currying”?
Pass, return, and partially apply functions. You practise Dart 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 Dart Academy?
No prior experience is required. Dart Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Higher-Order Functions and Currying” 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 Dart Academy lesson?
Yes. Every Dart 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
- Higher-Order Functions and Currying
- fold, reduce, and expand
- Lazy Iterables and Generators With sync*
- Composing Pure Function Pipelines