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- type: google.api.Service
- config_version: 3
- name: cel.googleapis.com
- title: Common Expression Language
- apis:
- - name: google.api.expr.v1alpha1.ConformanceService
- - name: google.api.expr.v1alpha1.CelService
- 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 }
- ```
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