You can use preprocessor symbols to control whether an assembly is compiled and included in builds of your application (including Play mode in the Editor). You can specify which symbols must be defined for an assembly to be used with the Define Constraints list in the Assembly Definition options:
For more information on which scripting symbols you can use for define constraints, refer to Define Constraints.
If you need to compile different code in an assembly according to whether a project uses specific versions of Unity or of a package, you can add entries to the Version Defines list. This list specifies rules for when a symbol should be defined. For version numbers, you can specify a logical expression that evaluates to a specific version or a range of versions.
To conditionally define a symbol:
Select the Assembly Definition asset for the assembly to view its properties in the Inspector.
In the Version Defines section, click the + button to add an entry to the list.
Set the properties:
The Version expression outcome shows which versions the expression evaluates to. If the outcome displays, Invalid, then the expression syntax is incorrect.
Click Apply.
Symbols defined in the Assembly Definition are only in scope for the scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary in the assembly created for that definition.
Note: You can use the symbols defined using the Version Defines list as Define Constraints. This means you can specify that an assembly is only used when specific versions of a given package are also installed in the project.
You can use expressions to specify an exact version or a range of versions.
A version expression uses mathematical interval notation, where square brackets [] designate that the range includes the endpoint and parentheses () designate that the range excludes the endpoint.
The following table illustrates the syntax:
| Expression | Evaluates to |
|---|---|
[1.3,3.4.1] |
1.3.0 <= x <= 3.4.1 |
(1.3.0,3.4) |
1.3.0 < x < 3.4.0 |
[1.1,3.4) |
1.1.0 <= x < 3.4.0 |
(0.2.4,5.6.2-preview.2] |
0.2.4 < x <= 5.6.2.-preview.2 |
[2.4.5] |
x = 2.4.5 |
2.1.0-preview.7 |
x >= 2.1.0-preview.7 |
Note: No spaces are allowed in an expression. No wildcard characters are supported.
Current versions of Unity (and all versions that support Assembly Definitions) use a version designator with three parts: MAJOR.MINOR.REVISION, for example, 6000.0.33f1.
MAJOR version is four digits representing the release year for Unity 2022.x.z and earlier, or the major technical version from Unity 6 (6000.x.z) onwards.MINOR version is the target release quarter, such as 1, 2, 3, or 4.REVISION designator has three parts of its own, with the format: RRzNN, where:
RR is a one or two digit revision numberz is a letter designating the release type:
a = alpha releaseb = beta releasef = a normal public releasec = China release version (equivalent to f)p = patch releasex = experimental releaseNN is a one or two digit incremental numberRelease type designators are compared as follows:
a < b < f = c < p < x
An alpha release is considered earlier than a beta, which is earlier than a normal (f) or China (c) release. A patch release is always later than a normal or China release with the same revision number and an experimental release is later than any other release type. Note that experimental releases do not use an incremental number at the end.
The following example expression includes any 6000.0 or 6000.1 version of Unity, but not any version in 6000.2 or later:
[6000.0,6000.2)
Package and module version designators have four parts, following the Semantic Versioning format: MAJOR.MINOR.PATCH-LABEL. The first three parts are always numbers, but the label is a string. Unity packages in preview use the string, preview or preview.n, where n > 0.
The following example expression includes all versions of a package with MAJOR.MINOR versions between 3.2 and 6.1 (inclusive):
[3.2,6.1]