targets property Null safety

A list of reflective targets.

Combined with metaTargets, this provides the complete list of reflective targets used by the library to which this metadata applies.

The following text is non-normative:

For now, there is no formal description of what a reflective target is. Informally, a target is a library, a class, a method or a field.

Dart2js currently supports the following formats to specify targets:

• A constant List containing String constants representing (qualified) names of targets and Dart types.
• A single String constant whose value is a comma-separated list of (qualified) names.
• A single Dart type.

A (qualified) name is resolved to a target as follows:

1. If the qualified name matches a library name, the matching library is the target.
2. Else, find the longest prefix of the name such that the prefix ends just before a . and is a library name.
3. Use that library as current scope. If no matching prefix was found, use the current library, i.e., the library where the MirrorsUsed annotation was placed.
4. Split the remaining suffix (the entire name if no library name was found in step 3) into a list of String using . as a separator.
5. Select all targets in the current scope whose name matches a String from the list.

For example:

library my.library.one;

class A {
  var aField;
}

library main;

@MirrorsUsed(targets: "my.library.one.A.aField")
import "dart:mirrors";

The MirrorsUsed annotation specifies A and aField from library my.library.one as targets. This will mark the class A as a reflective target. The target specification for aField has no effect, as there is no target in my.library.one with that name.

Note that everything within a target also is available for reflection. So, if a library is specified as target, all classes in that library become targets for reflection. Likewise, if a class is a target, all its methods and fields become targets for reflection. As a consequence, aField in the above example is also a reflective target.