Advanced Topics and Configuration

Language Features

In Q# projects, the JSON manifest (qsharp.json) has an optional languageFeatures property, which is an array of opt-in configurations for the compiler. Features will come and go, and they are typically introduced as a means for users to preview a feature before it is stable. Currently, there is only one language feature: v2-preview-syntax.

Features are written to be compatible with each other. That is, no features will be mutually exclusive, and a package that depends on other packages does not need to know what features are enabled in those packages -- they will always be compatible with the user code. See more details on the design of language features here.

v2-preview-syntax

Changes to Q# syntax are always backwards-compatible until a major version. Put another way, minor and patch releases of the QDK will never break Q# syntax -- changes will only ever be additive. The v2-preview-syntax feature will enforce the pending syntax changes that will be made official in major version 2 of Q#. This is useful for checking the compatibility of your codebase with the next major version of the QDK, or just to be prepared for any upcoming breaking changes.