Strings

Interpolation

${expr}

Inside a string literal, ${expression} inserts a value computed at runtime.

Program

Play the program to embed a computed age in a sentence.

interpolation.dart
Replay: real traced execution (multi-file project)
void main() {
  var name = 'Ada';
  var age = 36;
  print('${name} is ${age + 1} next year');
}

  1. name ← Ada

    1void main() {2  var name = 'Ada';3  var age = 36;
    values this stepAdaname

  2. age ← 36

    2var name = 'Ada';3var age = 36;4print('${name} is ${age + 1} next year');
    values this step36age

  3. print('${name} is ${age + 1} next year');

    3  var age = 36;4  print('${name} is ${age + 1} next year');5}
    outputAda is 37 next year
    values this stepAdaname36age

Follow the Values

  1. name starts as Ada.
  2. age starts as 36.
  3. ${name} inserts Ada into the string.
  4. ${age + 1} computes 37.
  5. The program prints Ada is 37 next year. | piece | value | | --- | --- | | ${name} | Ada | | ${age + 1} | 37 | | output | Ada is 37 next year |
$name Simple identifier interpolation.
${expr} Full-expression interpolation inside `${...}`.
immutable The original `name` and `age` are unchanged.

Exercise: interpolation.dart

Reproduce Ada is 37 next year, then trace how name Ada and age + 1 equals 37 create the sentence.