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# Dart Less Than
The `<` (less than) operator is a relational binary operator that evaluates whether the left operand is strictly smaller in value than the right operand, returning a `bool` (`true` or `false`).
In Dart, operators are implemented as instance methods. When the `<` operator is evaluated, Dart invokes the `operator <` method defined on the left operand's class, passing the right operand as the argument.
```dart theme={"dark"}
bool result = leftOperand < rightOperand;
```
## Built-in Type Behavior
For built-in numeric types (`num`, `int`, `double`), the `<` operator performs standard mathematical comparison. The Dart type system safely handles cross-type numeric comparisons (e.g., comparing an `int` to a `double`).
```dart theme={"dark"}
bool isLessNum = 5 < 10; // true
bool isLessMixed = 5.0 < 5; // false (strictly less than)
bool isLessNegative = -2 < -1; // true
```
*Note: Dart's `String` class does not define relational operators. Attempting to use `<` on strings will result in a compile-time error. To compare strings lexicographically, developers must use the `compareTo` method.*
## Operator Overloading
Because `<` is an instance method, it can be defined or overridden in custom classes to establish specific comparison semantics for objects. The method must return a `bool` and typically accepts a parameter of the same class type.
```dart theme={"dark"}
class Temperature {
final double celsius;
const Temperature(this.celsius);
// Overriding the < operator
bool operator <(Temperature other) {
return this.celsius < other.celsius;
}
}
void main() {
final t1 = Temperature(20.5);
final t2 = Temperature(30.0);
bool result = t1 < t2; // Evaluates to true
}
```
## Type Safety and Constraints
When defining the `<` operator, Dart's static analyzer enforces the parameter type declared in the method signature. If the right operand does not match the expected type, the compiler throws an error. For built-in types like `num`, the parameter is typed as `num`, preventing direct comparison with incompatible types like `String` or `bool`.
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