Functions and Records

Arrow Functions

=> Shorthand

When a function's body is a single expression, => is shorthand for { return expr; }. The block form and the arrow form behave identically; arrow is just more concise.

Program

Play the program to call a block-body and an arrow-body version of the same idea.

arrow_functions.dart
Replay: real traced execution (multi-file project)
int squareBlock(int n) {
  return n * n;
}

int squareArrow(int n) => n * n;

void main() {
  var a = squareBlock(5);
  var b = squareArrow(6);
  print('$a $b');
}

  1. call ← squareBlock(5)

    7void main() {8  var a = squareBlock(5);9  var b = squareArrow(6);
    values this stepsquareBlock(5)call

  2. return value ← 25

    1int squareBlock(int n) {2  return n * n;3}
    values this step25return value5n

  3. a ← 25

    7void main() {8  var a = squareBlock(5);9  var b = squareArrow(6);
    values this step25a

  4. call ← squareArrow(6)

    8var a = squareBlock(5);9var b = squareArrow(6);10print('$a $b');
    values this stepsquareArrow(6)call

  5. return value ← 36

    5int squareArrow(int n) => n * n;
    values this step36return value6n

  6. b ← 36

    8var a = squareBlock(5);9var b = squareArrow(6);10print('$a $b');
    values this step36b

  7. print('$a $b');

    9  var b = squareArrow(6);10  print('$a $b');11}
    output25 36
    values this step25a36b
arrow body `fn(x) => expr` is shorthand for `{ return expr; }` when the body is one expression.
implicit return There is no `return` keyword in an arrow body; the expression's value is returned.
equivalent semantics Block-body and arrow-body produce the same call result; arrow is just terser.