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Avoid runtime function type check in lazily created singleton creator functions #574

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merged 4 commits into from
Feb 7, 2022
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Avoid runtime function type check in lazily created singleton creator functions #574

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39c3249
Avoid runtime function type check in lazily created singleton creator…
mkustermann Jan 27, 2022
19a4a20
Suppress (bad) analyzer hint
mkustermann Jan 27, 2022
94e6b91
Make explicit downcast implicit to avoid cast in dart2js production mode
mkustermann Feb 7, 2022
62780fd
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mkustermann Feb 7, 2022
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38 changes: 23 additions & 15 deletions protobuf/lib/src/protobuf/generated_message.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -506,27 +506,35 @@ abstract class GeneratedMessage {

// Support for generating a read-only default singleton instance.

static final Map<Function?, Function> _defaultMakers = {};
static final Map<Function?, _SingletonMaker<GeneratedMessage>>
_defaultMakers = {};

static T Function() _defaultMakerFor<T extends GeneratedMessage>(
T Function()? createFn) {
return (_defaultMakers[createFn] ??= _createDefaultMakerFor<T>(createFn!))
as T Function();
}
T Function()? createFn) =>
_getSingletonMaker(createFn!)._frozenSingletonCreator;

static T Function() _createDefaultMakerFor<T extends GeneratedMessage>(
T Function() createFn) {
T? defaultValue;
T defaultMaker() {
return defaultValue ??= createFn()..freeze();
}
/// For generated code only.
static T $_defaultFor<T extends GeneratedMessage>(T Function() createFn) =>
_getSingletonMaker(createFn)._frozenSingleton;

return defaultMaker;
static _SingletonMaker<T> _getSingletonMaker<T extends GeneratedMessage>(
T Function() fun) {
final oldMaker = _defaultMakers[fun];
if (oldMaker != null) {
return oldMaker as _SingletonMaker<T>;
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To avoid check in dart2js production code, use an implicit downcast via:

    return oldMaker as dynamic;

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@mkustermann mkustermann Feb 7, 2022 •
edited
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Thanks for the suggestion. Done.

}
return _defaultMakers[fun] = _SingletonMaker<T>(fun);
}
}

/// For generated code only.
static T $_defaultFor<T extends GeneratedMessage>(T Function() createFn) =>
_defaultMakerFor<T>(createFn)();
class _SingletonMaker<T extends GeneratedMessage> {
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You should probably add a comment here explaining why we go this route (e.g. explain that we want to avoid any type checks against a function type and hence you an object container for functions).

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Done.

final T Function() _creator;

_SingletonMaker(this._creator);

late final T _frozenSingleton = _creator()..freeze();
// ignore: prefer_function_declarations_over_variables
late final T Function() _frozenSingletonCreator = () => _frozenSingleton;
}

/// The package name of a protobuf message.
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