This package contains the definition of
LookupMap: a simple, but very
restricted map. The map can only hold constant keys and the only way to use the
map is to retrieve values with a key you already have. Expect for lookup, any
other operation in
Map (like forEach, keys, values, length, etc) is not
LookupMaps are understood by dart2js and can be tree-shaken
internally: if a key is not used elsewhere in the program, its entry can be
deleted from the map during compilation without changing the program's behavior.
Currently dart2js supports tree-shaking keys that are Type literals, and any
const expression that can only be created with a const constructor. This means
that primitives, Strings, and constant objects that override the
cannot be tree-shaken.
Note: this feature is currently experimental in dart2js, we recommend trying other alternatives before relying on this feature.
LookupMap is unlikely going to be useful for individual developers writing
code by hand. It is mainly intended as a helper utility for frameworks that need
to autogenerate data and associate it with a type in the program. For example,
this can be used by a dependency injection system to record how to create
instances of a given type. A dependency injection framework can store in a
LookupMap all the information it needs for every injectable type in every
library and package. When compiling a specific application, dart2js can
tree-shake the data of types that are not used by the application. Similarly,
this can also be used by serialization/deserialization packages that can store
LookupMap the deserialization logic for a given type.