Module activation

Activation context for expression evaluation.

This module provides the Activation type, which serves as the runtime context for CEL expression evaluation. Activations contain variable bindings and function implementations that are used during expression evaluation.

Key Concepts

Activation Interface

The ActivationInterface trait defines the contract for providing variable and function bindings to the CEL evaluator. It provides access to:

• Variable bindings: Map variable names to runtime values
• Function bindings: Provide runtime function implementations

Activation Types

The module provides several activation types:

• Activation<'f>: Standard activation for synchronous evaluation
• AsyncActivation<'f>: Activation with async function support
• (): Empty activation for expressions without variables/functions

Variable Binding

Variables can be bound to values that match the types declared in the environment:

use cel_cxx::*;

let activation = Activation::new()
    .bind_variable("user_name", "Alice".to_string())?
    .bind_variable("user_age", 30i64)?
    .bind_variable("is_admin", true)?;

Function Binding

Functions can be bound at runtime to override or supplement environment functions:

use cel_cxx::*;

let activation = Activation::new()
    .bind_global_function("custom_add", |a: i64, b: i64| a + b)?
    .bind_member_function("to_upper", |s: String| s.to_uppercase())?;

Variable Providers

For dynamic or computed values, you can bind variable providers:

use cel_cxx::*;

let activation = Activation::new()
    .bind_variable_provider("current_time", || {
        std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap()
            .as_secs() as i64
    })?;

Empty Activations

For expressions that don’t require any bindings, you can use the unit type:

use cel_cxx::*;

let env = Env::builder().build()?;
let program = env.compile("1 + 2 * 3")?;
let result = program.evaluate(())?; // No activation needed

Async Support

When the async feature is enabled, activations can contain async functions:

use cel_cxx::*;

let activation = AsyncActivation::new_async()
    .bind_global_function("fetch_data", |url: String| async move {
        // Simulate async work
        format!("Data from {}", url)
    })?;

Structs

Activation

Activation context for CEL expression evaluation.

Traits

ActivationInterface

Interface for providing variable and function bindings during evaluation.

Type Aliases

AsyncActivationasync

Activation with async support.