type: google.api.Service
config_version: 3
name: cel.googleapis.com
title: Common Expression Language
apis:
- name: google.api.expr.v1alpha1.ConformanceService
documentation:
summary: Defines common types for the Common Expression Language.
overview: |-
# Common Expression Language
The Common Expression Language (CEL) implements common semantics for
expression evaluation, enabling different applications to more easily
interoperate.
Key Applications
* Security policy: organization have complex infrastructure and need
common tooling to reason about the system as a whole * Protocols:
expressions are a useful data type and require interoperability across
programming languages and platforms.
Guiding philosophy:
1. Keep it small & fast.
* CEL evaluates in linear time, is mutation free, and not
Turing-complete. This limitation is a feature of the language
design, which allows the implementation to evaluate orders of
magnitude faster than equivalently sandboxed JavaScript. 2. Make
it extensible.
* CEL is designed to be embedded in applications, and allows for
extensibility via its context which allows for functions and data
to be provided by the software that embeds it. 3.
Developer-friendly
* The language is approachable to developers. The initial spec was
based on the experience of developing Firebase Rules and usability
testing many prior iterations. * The library itself and
accompanying toolings should be easy to adopt by teams that seek
to integrate CEL into their platforms.
The required components of a system that supports CEL are:
* The textual representation of an expression as written by a developer.
It is of similar syntax of expressions in C/C++/Java/JavaScript * A
binary representation of an expression. It is an abstract syntax tree
(AST).
* A compiler library that converts the textual representation to the
binary representation. This can be done ahead of time (in the control
plane) or just before evaluation (in the data plane). * A context
containing one or more typed variables, often protobuf messages. Most
use-case will use attribute_context.proto
* An evaluator library that takes the binary format in the context and
produces a result, usually a Boolean.
Example of boolean conditions and object construction:
``` c
// Condition
account.balance >= transaction.withdrawal
|| (account.overdraftProtection
&& account.overdraftLimit >= transaction.withdrawal -
account.balance)
// Object construction
common.GeoPoint{ latitude: 10.0, longitude: -5.5 }
```