cty

Warning

This is a temporary fork created specifically for github.com/hashicorp/packer-plugin-sdk. Usage beyond that is considered unsupported and subject to break when the fork is deleted.

Usage of this fork within the Packer plugin SDK is needed, while Packer moves away from encoding/gob for cty.Value and cty.Type. Changes from upstream will be ported on a as needed basis.

cty (pronounced "see-tie", emoji: 👀 👔, IPA: /si'tʰaɪ/) is a dynamic type system for applications written in Go that need to represent user-supplied values without losing type information. The primary intended use is for implementing configuration languages, but other uses may be possible too.

One could think of cty as being the reflection API for a language that doesn't exist, or that doesn't exist yet. It provides a set of value types and an API for working with values of that type.

Fundamentally what cty provides is equivalent to an interface{} with some dynamic type information attached, but cty encapsulates this to ensure that invariants are preserved and to provide a more convenient API.

As well as primitive types, basic collection types (lists, maps and sets) and structural types (object, tuple), the cty type and value system has some additional, optional features that may be useful to certain applications:

• Representation of "unknown" values, which serve as a typed placeholder for a value that has yet to be determined. This can be a useful building-block for a type checker. Unknown values support all of the same operations as known values of their type, but the result will often itself be unknown.

• Representation of values whose types aren't even known yet. This can represent, for example, the result of a JSON-decoding function before the JSON data is known.

Along with the type system itself, a number of utility packages are provided that build on the basics to help integrate cty into calling applications. For example, cty values can be automatically converted to other types, converted to and from native Go data structures, or serialized as JSON.

For more details, see the following documentation:

• Concepts
• Full Description of the cty Types
• API Reference (godoc)
• Conversion between cty types
• Conversion to and from native Go values
• JSON serialization
• cty Functions system
• Compatibility Policy for future Minor Releases: please review this before using cty in your application to avoid depending on implementation details that may change.

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License

Copyright 2017 Martin Atkins

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.