Dart: String Interpolation

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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.

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!

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