TemplateExpressionEvaluator class abstract interface

Evaluates expressions in the context of a template, returning a boolean result that indicates whether the expression is truthy.

An TemplateExpressionEvaluator is used within template engines to support conditional rendering, loops, or dynamic content based on the values in a TemplateContext.

Responsibilities

• Parse and evaluate expressions provided as strings.
• Resolve variables and values using a TemplateContext.
• Return a boolean indicating whether the expression is considered "truthy".
• Support template logic such as if statements, for loops, or custom conditional directives.

Design Notes

• Implementations may use expression parsing libraries, regex evaluation, or custom interpreters.
• Should handle unknown variables gracefully, e.g., treat missing variables as null or false, depending on the template logic.
• Can be extended to support operators, comparisons, and functions within template expressions.

Usage Example

final evaluator = MyExpressionEvaluator();
final context = MyTemplateContext({'isLoggedIn': true});

final result = evaluator.evaluate('isLoggedIn', context);
print(result); // true

final result2 = evaluator.evaluate('user.age > 18', context);
print(result2); // true or false depending on context

Properties

hashCode → int

The hash code for this object.

no setter, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

evaluate(String expression, TemplateContext context) → bool

Evaluates the given expression string using the provided context.

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited