Lesson 05 of 59

5 mins read

String Interpolation, Multiline & Raw Strings

In Plain English

Strings in Dart are immutable sequences of UTF-16 code units. String interpolation allows seamless embedding of variables (`$name`) and complex expressions (`${cart.total * 1.08}`) directly inside string literals without ugly string concatenation. Dart also supports multiline strings (`"""..."""`) and raw strings (`r"\n"`).

The Mental Model

"String interpolation is like a fill-in-the-blank template: the template sentence is clear, and the dynamic variables fill into the blanks automatically."

Deep Dive: How It Works

Simple Variable Interpolation: `$variable` evaluates and casts the variable to string.

Complex Expression Interpolation: `${object.property.toUpperCase()}` evaluates any valid Dart expression inside the braces.

Raw Strings: Prefixing with `r` (`r"C:\path\new"`) disables escape sequence interpretation.

Multiline Strings: Triple single/double quotes (`"""..."""`) preserve newlines and indentation.

Syntax Blueprint

var msg = "Item: $name, Price: ${price * 1.1}";
var multi = """\nLine 1\nLine 2\n""";
var raw = r"No \n escape interpretation";

Expressive string creation patterns in modern Dart.

Core Rules to Remember

Expression Interpolation: Use `${...}` to embed method calls and arithmetic directly in strings.

No String Concatenation: Avoid `+` operators; adjacent string literals automatically concatenate at compile-time.

Raw Strings (r""): Essential for regular expressions and Windows file paths.

Common Beginner Traps & How to Fix Them

Mistake:Using `${var}` for simple variables instead of `$var`.

Why it happens: Both work, but `$var` is cleaner and the idiomatic Dart style.

How to fix: Use `$name` for simple identifiers and `${user.name}` only when accessing properties or methods.

Pro Tip: Adjacent string literals like `var s = 'Hello ' 'World';` are merged by the compiler at zero runtime cost.

Live Interactive Example

Hit Run Code to see it live

String Interpolation and Multiline Strings in Action

Python 3.12

Output Console

Click "Run Code" to view the rendered output.

How it works: Interpolated expressions and ternary operators cleanly formatted inside a multiline string template.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Format Product Summary

Given `String product = "Flutter Book";` and `double price = 39.95;`.
Print `Product: $product costs $$price (Discount: ${price * 0.9})`.

Sandbox Output

Click "Run & Check" to test your solution.

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