Dart: String Interpolation

Imagine you’re writing a letter to your friend, and you want to include their name in it. Instead of writing:

“Hello, [friend’s name]!”

Wouldn’t it be great if you could just tell Dart to fill in the name for you? That’s exactly what string interpolation does!

String interpolation is a fancy way of saying “put variables inside a string.” Instead of using long and messy ways to combine text, Dart lets us insert values directly into a string in a simple and clean way.

In this article, we’ll explore how to use string interpolation to make working with text easier.

Table of Contents

Basic String Interpolation

The easiest way to insert a variable into a string is by using the $ symbol.

Example: Adding a Name and Age to a String

void main() {

  String name = "Edward";
  int age = 20;

  print("Hello, my name is $name and I am $age years old.");

}

What’s Happening Here?

Dart sees the $name and replaces it with “Edward”.
It sees $age and replaces it with 20.

This is much cleaner than writing something like:

print("Hello, my name is " + name + " and I am " + age.toString() + " years old.");

Interpolation helps avoid using extra plus signs (+) and conversions, making the code easier to read.

Using Expressions in Interpolation

What if we need to do some math inside a string? That’s where ${} comes in!

If you need to perform calculations or call functions inside a string, wrap the expression inside ${}.

Example: Doing Math Inside a String

void main() {

  int apples = 3;
  int bananas = 5;

  print("I have ${apples + bananas} fruits in total.");

}

Wha’s Happening Here?

Dart sees ${apples + bananas} and calculates 3 + 5 = 8.
It replaces the expression with 8, so the output is:

I have 8 fruits in total.

You can also call functions inside interpolation!

String upperCaseName(String name) {
  return name.toUpperCase();
}

void main() {

  String name = "Edward";
  print("My name in uppercase is ${upperCaseName(name)}.");

}

Dart replaces ${upperCaseName(name)} with EDWARD!

Handling Special Cases

Escaping Dollar Signs (`\$`)

What if you actually want to show a dollar sign ($) in your string, like for money? You can use a backslash (\) before the dollar sign (\$).

void main() {

  int price = 50;

  print("This book costs \$${price}.");

}

Without the backslash, Dart might think $price is a variable!

Multiline String Interpolation

Dart also allows multiline strings using triple quotes (""" or '''). This is useful when formatting long text with interpolation.

void main() {

  String name = "Edward";
  int age = 20;

  String introduction = """Hello!
My name is $name.
I am $age years old.""";

  print(introduction);

}

This makes text more readable instead of using multiple print statements.

Conclusion

You now understand how to use string interpolation in Dart! You’ve learned:

How to insert variables into a string using $variable.
How to use ${expression} for calculations and function calls.
How to handle special cases like escaping $ and working with multiline strings.

String interpolation makes your code more readable and efficient. Try using it in your own programs to simplify text handling and improve clarity!